Bodily Oddities
A comprehensive catalog of 155 sourced things normal human bodies (sometimes) do, compiled and adapted from Bodily Oddities by Vester. Explore the full collection of sensory illusions, involuntary quirks, motor tricks, vestigial reflexes, and rare genetic variations below.
Anatomical Regions Overview
🧠 Group 1: Brain (37 oddities)
Perceptions, illusions, altered states, and cognitive quirks.👁️ Group 2: Eyes & Vision (29 oddities)
Entoptic phenomena, visual illusions, pupil reflexes, and ocular adaptations.👂 Group 3: Ears & Hearing (14 oddities)
Auditory clicks, middle-ear muscle rumbles, phantom sounds, and anatomical traits.👄 Group 4: Mouth & Throat (14 oddities)
Tongue mobility tricks, palate variations, taste perception, and airway reflexes.👃 Group 5: Nose & Olfaction (5 oddities)
Reflexive drips, flaring muscles, and olfactory variations.🧬 Group 6: Skin & Hair (9 oddities)
Piloerection, tactile writing, dermatological traits, and water wrinkles.💪 Group 7: Muscles & Tendons (8 oddities)
Vestigial tendons, involuntary twitches, and voluntary muscle control.🦴 Group 8: Bones & Joints (13 oddities)
Hypermobility, accessory bones, joint cavitation, and skeletal variations.🫀 Group 9: Heart & Blood (5 oddities)
Vascular reflexes, blood shifting, syncope, and cardiac control.🫁 Group 10: Internal Organs & Digestion (6 oddities)
Gastrointestinal sounds, kidney diuresis, diaphragm spasms, and visceral mechanics.⚡ Group 11: Nervous System & Reflexes (12 oddities)
Primitive reflexes, sensory misdirection, and neural wiring quirks.🧍 Group 12: Whole Body & Genetics (3 oddities)
Systemic genetic variations, chimerism, mirror anatomy, and rare physiological traits.
Group 1: 🧠 Brain (37 oddities)
Perceptions, illusions, altered states, and cognitive quirks.
Alice in Wonderland syndrome ↗
Prevalence: 6–7% of teenagers (size distortion) · Kind: Perception · System: Brain, Eyes & Vision
Also known as: AIWS, Todd's syndrome, Micropsia and macropsia, Tachysensia, Fast feeling
Objects, body parts, or the whole room suddenly look far too big, far too small, or far away. It mostly happens to children, often during a fever or infection, and it passes on its own. In adults it is often linked to migraine.
🏷️ childhood not-an-emergency illusion community
Ambidexterity ↗
Prevalence: About 1% · Kind: Trick · System: Brain, Muscles & Tendons
Also known as: True ambidexterity
Using both hands equally well for every task. About 1% of people are truly ambidextrous. Many people who say they are ambidextrous are mixed-handed: right hand for some jobs, left for others.
🏷️ learnable genetic famous-people try-it
Aphantasia ↗
Prevalence: About 1% have no mental images. About 4% have faint or none. · Kind: Perception · System: Brain
Also known as: Congenital aphantasia
Most people see a picture in their mind when they think of a friend's face. People with aphantasia see only a faint image or none. About 4 in 100 people are like this, and about 1 in 100 see nothing at all. A few people have images almost as vivid as real sight.
🏷️ try-it genetic famous-people community
ASMR ↗
Prevalence: Unclear; estimates 20–60% · Kind: Involuntary · System: Brain, Skin & Hair
Also known as: Autonomous sensory meridian response, "Brain tingles"
A pleasant tingling that starts on the scalp and moves down the neck and spine, set off by whispering, tapping, soft sounds, or gentle personal attention. Not everyone gets it. A large online community is built around it.
🏷️ community
Brain zaps ↗
Prevalence: 15–50% of people stopping an antidepressant get withdrawal symptoms · Kind: Involuntary · System: Brain, Nervous System & Reflexes
Also known as: Brain shivers, Brain shocks, Electrical shock sensations
A brief feeling like a small electric shock inside the head, often set off by moving the eyes. It is most common when stopping or lowering an antidepressant. It is unpleasant, but usually not a problem.
🏷️ not-an-emergency
Call of the void ↗
Prevalence: 43–60% of people · Kind: Involuntary · System: Brain
Also known as: L'appel du vide, High place phenomenon
A sudden, brief thought of jumping when you stand somewhere high, with no wish to do it. About half of people get it. It is probably the brain's safety system being misread, not a hidden wish.
🏷️ not-an-emergency
Charles Bonnet syndrome ↗
Prevalence: 10–40% of older people with serious sight loss · Kind: Perception · System: Brain, Eyes & Vision
Also known as: CBS, Visual release hallucinations
People who lose a lot of their sight often start to see things that are not there: patterns, faces, small people in costume, whole landscapes. They know the images are not real. It is caused by sight loss, not by mental illness.
🏷️ not-an-emergency illusion
Chronostasis ↗
Prevalence: Everyone · Kind: Perception · System: Brain, Eyes & Vision
Also known as: Stopped clock illusion, Stopped-clock illusion
Glance at a clock and the second hand can seem to freeze for a moment before it moves. The brain hides your eye movement and stretches the first thing you see to cover the gap.
🏷️ try-it illusion
Contagious yawning ↗
Prevalence: About 30–70% of adults · Kind: Reflex · System: Brain
Also known as: Yawn contagion
Seeing, hearing, or even reading about a yawn makes many adults yawn. The effect appears in early childhood, may be linked to empathy, and crosses over to dogs.
🏷️ try-it
Déjà vu ↗
Prevalence: About 2 in 3 people · Kind: Involuntary · System: Brain
Also known as: "Already seen", Paramnesia
A strong feeling that you have lived the present moment before, even though you know you have not. About two in three people get it. It peaks between the ages of 15 and 25.
🏷️ illusion childhood
Derealization and depersonalization ↗
Prevalence: 26–74% of people, at least once · Kind: Involuntary · System: Brain
Also known as: DPDR
The world suddenly seems flat, distant, or like a film (derealization), or you feel like you are watching yourself from outside (depersonalization). Many people have a brief episode at some point, usually under stress.
🏷️ not-an-emergency community
Eidetic memory ↗
Prevalence: 2–10% of children aged 6–12 · Kind: Rare Ability · System: Brain
Also known as: Photographic memory (popular term)
Some children can keep a detailed picture of an image in view for a short time after it is taken away. The ability fades by the teenage years. A true photographic memory in adults has never been confirmed.
🏷️ debunked-myth childhood
Exploding head syndrome ↗
Prevalence: 2–37% of people, lifetime · Kind: Involuntary · System: Brain, Ears & Hearing
Also known as: Episodic cranial sensory shock
A loud bang, crash, or explosion heard inside the head while falling asleep or waking up. Nothing actually happens, there is no pain, and it is harmless.
🏷️ not-an-emergency sleep
Frisson ↗
Prevalence: Reported rates vary between studies · Kind: Involuntary · System: Brain, Skin & Hair
Also known as: Music chills, Aesthetic chills
A wave of chills up the back, sometimes with goosebumps, at a powerful moment in music, a film, or a speech. It is thought to come from the brain's reward system reacting to an expectation being met or broken.
🏷️ community
Ganzfeld effect ↗
Prevalence: Most people who try it, in lab tests · Kind: Perception · System: Brain, Eyes & Vision
Also known as: Perceptual deprivation
Fill your whole field of view with a featureless colour and, after some minutes, your brain may start inventing shapes, lights, and scenes. Two halved ping-pong balls and a lamp are enough to do it at home.
🏷️ try-it illusion spiritual
Geometric nightmares ↗
Prevalence: Not known · Kind: Perception · System: Brain
Also known as: Geometric fever dreams, Fever geometry
A kind of dream, often during fever in childhood, filled with huge or tiny shapes, infinite space, crushing pressure, and dread. The name comes from an online forum, not a medical text, but each piece of it is well known to neuroscience.
🏷️ childhood sleep community illusion
Highly superior autobiographical memory ↗
Prevalence: Fewer than 100 confirmed cases · Kind: Rare Ability · System: Brain
Also known as: HSAM, Hyperthymesia
Fewer than a hundred people worldwide have been confirmed to recall what happened on almost any date since about age 10, in detail and without effort. Their memory for other things, such as lists or numbers, is ordinary.
🏷️ famous-people record
Human echolocation ↗
Prevalence: Nobody has counted it · Kind: Rare Ability · System: Brain, Ears & Hearing
Also known as: Flash sonar, Click echolocation
Some blind people find their way by making sharp tongue clicks and listening to the echoes. Brain scans show the echoes are processed in the visual cortex. Sighted people can learn a basic version in ten weeks of training.
🏷️ learnable famous-people try-it
Hypnagogic hallucinations ↗
Prevalence: About 25–37% of people · Kind: Involuntary · System: Brain
Also known as: Hypnopompic hallucinations, Sleep-onset hallucinations
Vivid images, sounds, or touches that appear while you are falling asleep or waking up. A face, a voice saying your name, a hand on your shoulder. They may be dream fragments arriving early or late, and they are usually normal.
🏷️ not-an-emergency sleep
Hypnic jerks ↗
Prevalence: About 70% of people · Kind: Involuntary · System: Brain, Muscles & Tendons
Also known as: Sleep starts, Hypnagogic jerks
A sudden jolt of the arms, legs, or whole body just as you fall asleep, sometimes with a feeling of falling. Most people get them, and they are harmless.
🏷️ not-an-emergency sleep
Jamais vu ↗
Prevalence: Unknown. Thought to be rarer than déjà vu. · Kind: Involuntary · System: Brain
Also known as: "Never seen"
A familiar word, face or place suddenly feels strange, as if you are meeting it for the first time. It is the opposite of déjà vu, and researchers think it is rarer. In lab studies, more than half of people felt a common word turn strange after copying it about 30 times.
🏷️ try-it illusion
Meditation body dissolution ↗
Prevalence: About 29% of recent meditators · Kind: Perception · System: Brain, Nervous System & Reflexes
Also known as: Self-boundary dissolution, Body boundary loss
During long, still meditation the brain loses track of the edges of the body. The body can feel indistinct or seem to expand into space. Flotation tanks produce the same effect. It is usually harmless.
🏷️ spiritual illusion
Migraine aura ↗
Prevalence: About 5% of people · Kind: Involuntary · System: Brain, Eyes & Vision
Also known as: Ocular migraine, Scintillating scotoma, Migraine aura without headache, Silent migraine, Fortification spectra
A change in vision that builds over minutes and usually fades within an hour. The best-known form is a shimmering zigzag, but auras vary a lot: flashes, fog, blind patches or static. It can come before a migraine, or alone.
🏷️ get-it-checked
Mirror-touch synesthesia ↗
Prevalence: About 1.6% of people · Kind: Rare Ability · System: Brain, Nervous System & Reflexes
Also known as: Mirror-touch synaesthesia
About 1 in 60 people feel a touch on their own body when they watch someone else being touched. The brain system that mirrors other people's actions appears to be turned up too high.
🏷️ debunked-myth
Motion aftereffect ↗
Prevalence: Everyone · Kind: Perception · System: Brain, Eyes & Vision
Also known as: Waterfall illusion, Motion after-effect
Watch something move in one direction for about a minute, then look at something still. The still thing appears to drift the opposite way for a few seconds.
🏷️ try-it illusion
Musical ear syndrome ↗
Prevalence: 3.6% of people sent for a hearing test · Kind: Sound · System: Brain, Ears & Hearing
Also known as: Musical hallucinations, Auditory Charles Bonnet syndrome
Some people with hearing loss hear clear, complete music that no one is playing. The brain replays stored songs to fill the silence. Most people with it know the music is not real.
🏷️ illusion
Night terrors ↗
Prevalence: About 1 in 3 young children · Kind: Involuntary · System: Brain
Also known as: Sleep terrors, Pavor nocturnus
A sleeping child suddenly sits up, screams, and looks terrified, but is not awake. Parts of the brain act awake while the rest stays in deep sleep. Next morning the child usually remembers nothing. The parent remembers all of it.
🏷️ sleep childhood not-an-emergency
Perfect pitch ↗
Prevalence: Often quoted as 1 in 10,000 people · Kind: Rare Ability · System: Brain, Ears & Hearing
Also known as: Absolute pitch, AP
An often-quoted estimate is that 1 in 10,000 people can name or sing any musical note without hearing a reference note first. It runs in families and is far more common in people who started music lessons very young.
🏷️ genetic
Phantom phone vibrations ↗
Prevalence: 30–89% of phone users · Kind: Involuntary · System: Brain, Nervous System & Reflexes
Also known as: Phantom vibration syndrome, Ringxiety, Fauxcellarm
You feel your phone buzz in your pocket, check it, and nothing happened. Most phone users get this. The cause is not known. The brain may misread ordinary sensations as a buzz.
🏷️ illusion
Prisoner's cinema ↗
Prevalence: 77% of sighted people blindfolded for four days · Kind: Perception · System: Brain, Eyes & Vision
Also known as: Sensory deprivation hallucinations
After hours or days in darkness, people start to see light shows: colours, geometric patterns, and sometimes figures or scenes. Prisoners, truck drivers, pilots, and meditators all report it.
🏷️ illusion spiritual
Prosopagnosia ↗
Prevalence: About 1–2.5% of people · Kind: Perception · System: Brain
Also known as: Face blindness, Developmental prosopagnosia, Congenital prosopagnosia
People with prosopagnosia, or face blindness, find it hard to recognise faces, even those of family and friends. Most have had it all their lives. It can also start after brain damage. Estimates run from about 1 in 100 people to about 1 in 40, depending on how it is tested.
🏷️ try-it genetic famous-people community
Rubber hand illusion ↗
Prevalence: 60–80% of participants · Kind: Involuntary · System: Brain
Stroke a rubber hand and a person's hidden real hand at the same time, and within a minute or two the brain adopts the rubber hand as its own. It shows that your sense of your body is built moment by moment from sight and touch.
🏷️ illusion try-it
Short sleeper syndrome ↗
Prevalence: Nobody has counted it · Kind: Rare Ability · System: Brain, Whole Body & Genetics
Also known as: Familial natural short sleep, FNSS
A small number of people need only 4 to 6 hours of sleep a night, wake without an alarm, and feel fine. Several gene variants have been linked to it. Most people who sleep that little are probably sleep-deprived.
🏷️ genetic
Sleep paralysis ↗
Prevalence: 8–30% of people · Kind: Involuntary · System: Brain, Muscles & Tendons
Also known as: Isolated sleep paralysis, Old Hag syndrome, Kanashibari
You wake up, or start to fall asleep, and cannot move or speak for a few seconds to minutes. Sometimes a threatening presence seems to be in the room. It is the normal paralysis of dreaming sleep running a little late.
🏷️ not-an-emergency sleep community
Strange-face illusion ↗
Prevalence: 66% see their face distort · Kind: Perception · System: Brain, Eyes & Vision
Also known as: Strange-face-in-the-mirror illusion, Mirror-gazing illusion
Stare at your own face in a mirror in dim light for a few minutes and it starts to distort. Most people see their features warp. Some see a stranger, an animal, or a monster.
🏷️ try-it illusion
Synesthesia ↗
Prevalence: About 4% of people · Kind: Perception · System: Brain
Also known as: Synaesthesia, Grapheme-colour synesthesia, Chromesthesia
In some people, one sense triggers another. Letters have colours, sounds have shapes, or days of the week sit in fixed places in space. The pairings are automatic and stay largely the same over many years.
🏷️ genetic famous-people community
Visual snow ↗
Prevalence: About 2% of people · Kind: Involuntary · System: Brain, Eyes & Vision
Also known as: Visual snow syndrome, Static
Tiny flickering dots across the whole field of vision, like static on an old TV, present with eyes open or closed. About 2% of people have it. The eyes are fine. The visual part of the brain is over-active.
🏷️ get-it-checked community
Group 2: 👁️ Eyes & Vision (29 oddities)
Entoptic phenomena, visual illusions, pupil reflexes, and ocular adaptations.
Accommodation reflex ↗
Prevalence: Everyone · Kind: Reflex · System: Eyes & Vision, Nervous System & Reflexes
Also known as: Near reflex, Accommodation-convergence reflex
When you look at something close, three things happen at once. The eyes turn inward, the pupils shrink, and the lens in each eye gets fatter. You do not have to decide any of it.
Afterimages ↗
Prevalence: Everyone · Kind: Perception · System: Eyes & Vision, Brain
Also known as: Positive afterimage, Negative afterimage, Ghost image
An image that stays in your vision after the thing you looked at is gone. Bright things leave a same-colour copy for a moment. Long stares leave a copy in opposite colours.
🏷️ try-it illusion
Anisocoria ↗
Prevalence: About 1 in 5 people at any one time, in dim light · Kind: Variation · System: Eyes & Vision, Nervous System & Reflexes
Also known as: Unequal pupils, Physiological anisocoria, Simple anisocoria
Pupils of two different sizes. In dim light, about 1 in 5 healthy people have a small, measurable difference at any one time, often too small to spot by eye. A difference that appears suddenly is not the same thing and needs urgent care.
🏷️ get-it-checked famous-people
Blue arcs of the retina ↗
Prevalence: 94% of healthy eyes in one clinic test · Kind: Perception · System: Eyes & Vision
Also known as: Blue arc phenomenon, Purkinje's blue arcs
Look at a small red light in a dark room and two faint blue arcs curve away from it towards your blind spot. The arcs follow the paths of the nerve fibres in your own retina.
🏷️ try-it
Blue field entoptic phenomenon ↗
Prevalence: Most people · Kind: Perception · System: Eyes & Vision
Also known as: Scheerer's phenomenon, Blue sky sprites
Tiny bright dots that dart along wiggly paths when you look at a clear blue sky. They are your own white blood cells moving through the capillaries of the retina.
🏷️ try-it
Closed-eye hallucinations ↗
Prevalence: Almost everyone · Kind: Perception · System: Eyes & Vision, Brain
Also known as: Closed-eye visualizations, CEV
Close your eyes and you do not see nothing. You see speckle, drifting colour, and, as you fall asleep, moving patterns and even scenes. Almost everyone sees the speckle, and many people see more. Almost nobody talks about them.
🏷️ try-it sleep spiritual
Crossing your eyes ↗
Prevalence: Most people (no formal count) · Kind: Trick · System: Eyes & Vision, Muscles & Tendons
Also known as: Voluntary convergence, Going cross-eyed
Turning both eyes inward toward the nose on purpose. Most people with normal two-eyed vision can do it. Your eyes will not get stuck that way.
🏷️ try-it debunked-myth party-trick
Distichiasis ↗
Prevalence: About 1 in 10,000 people · Kind: Variation · System: Eyes & Vision, Skin & Hair
Also known as: Double eyelashes, Double row of eyelashes
A second row of eyelashes growing from the oil-gland openings along the inner edge of the eyelid. It is rare. It can be inherited or acquired. Elizabeth Taylor was born with it.
🏷️ genetic famous-people get-it-checked
Eigengrau ↗
Prevalence: Everyone · Kind: Perception · System: Eyes & Vision
Also known as: Brain grey, Intrinsic grey, Dark light
The colour you see in total darkness is not black. It is a very dark grey, most likely because the light-sensing cells in your eyes fire a little even when no light reaches them.
🏷️ try-it
Emotional tears ↗
Prevalence: Almost everyone · Kind: Reflex · System: Eyes & Vision
Also known as: Psychic tears, Psychic lacrimation, Crying
Humans are the only animals known to weep from feeling. Emotional tears have a different chemistry from the tears that wash the eye, and babies cannot make them until one or two months after birth.
Eyelid flipping ↗
Prevalence: No formal count · Kind: Trick · System: Eyes & Vision, Skin & Hair
Also known as: Eyelid eversion, Lid eversion
Turning the upper eyelid inside out so the pink inner surface shows. Nobody has counted how many people can do it. Eye doctors do it to patients to look for grit.
🏷️ icky try-it learnable party-trick
Floaters ↗
Prevalence: 76% in one survey of 603 people · Kind: Involuntary · System: Eyes & Vision
Also known as: Muscae volitantes, Eye floaters, Vitreous floaters, Myodesopsia, Myiodesopsia
Small grey threads, dots, or cobwebs that drift across your vision and dart away when you look at them. They are shadows of tiny clumps inside the eye. They are common and usually harmless.
🏷️ get-it-checked
Foveal tritanopia ↗
Prevalence: Everyone · Kind: Perception · System: Eyes & Vision
Also known as: Small-field tritanopia, Central blue blindness
The very centre of your vision cannot see blue. The middle of the fovea has no blue-sensitive cones at all. You never notice, because the brain fills the colour in from the surrounding area.
🏷️ illusion
Haidinger's brush ↗
Prevalence: Most people, with practice · Kind: Perception · System: Eyes & Vision
Also known as: Haidinger's brushes, Polarization brush
Humans can see the polarization of light without any tool. It appears as a faint yellow bow-tie in the middle of your vision when you look at a white screen or a blue sky.
🏷️ try-it learnable
Heterochromia ↗
Prevalence: Fewer than 200,000 people in the US · Kind: Variation · System: Eyes & Vision
Also known as: Heterochromia iridum, Odd eyes
Eyes of two different colours, or one eye with two colours, in fewer than 1 in 100 people. When it is present from birth it is usually harmless.
🏷️ genetic famous-people debunked-myth
Independent eye movement ↗
Prevalence: No formal count · Kind: Trick · System: Eyes & Vision, Brain
Also known as: Disconjugate eye movement, Moving one eye at a time
Moving one eye while the other stays still, or moving the two eyes in different directions. Few people seem to manage it, and nobody has counted them. Chameleons do it all day.
🏷️ party-trick try-it
Palinopsia ↗
Prevalence: Not counted in the general population · Kind: Perception · System: Eyes & Vision, Brain
Also known as: Visual trailing, Visual echoes, Illusory palinopsia
An image that keeps appearing after the thing you saw is gone. A faint afterimage after a bright light is normal and harmless. Copies that persist or return later need a doctor.
🏷️ get-it-checked illusion
Phosphenes ↗
Prevalence: Anyone with a working retina · Kind: Involuntary · System: Eyes & Vision, Brain
Also known as: Pressure phosphenes, "Seeing stars"
The flashes, rings, and patterns of light you see when you rub or press your closed eyes, or after a knock on the head. Pressure on the eye makes the retina fire without any light.
🏷️ try-it illusion
Pupillary light reflex ↗
Prevalence: Everyone · Kind: Reflex · System: Eyes & Vision, Nervous System & Reflexes
Also known as: Photopupillary reflex, Pupil reflex
Shine a light into one eye and both pupils shrink, even the eye in the dark. The wiring crosses in the midbrain so that the two pupils react together. You can watch it in a mirror.
🏷️ try-it
Purkinje effect ↗
Prevalence: Everyone · Kind: Perception · System: Eyes & Vision
Also known as: Purkinje shift, Purkinje phenomenon
As the light fades at dusk, red things go dark first and blue things stay bright. Your eyes switch from colour-sensing cones to blue-favouring rods, and the whole world shifts towards blue.
🏷️ try-it
Purkinje images ↗
Prevalence: Everyone · Kind: Perception · System: Eyes & Vision
Also known as: Purkinje-Sanson images, Catoptric images
A candle held near someone's eye produces four tiny reflections, one from each surface of the cornea and lens. Eye trackers and eye doctors use them. In the right conditions you can see two of them inside your own eye.
Purkinje tree ↗
Prevalence: Everyone · Kind: Perception · System: Eyes & Vision
Also known as: Retinal vascular figure, Purkinje's tree, Purkinje figure
A branching shadow of your own retinal blood vessels. It is always on your retina, but you only see it when light enters the eye from an unusual angle and the shadow moves.
🏷️ try-it
Seeing flashes from sounds ↗
Prevalence: 57% of 77 students after sitting in the dark · Kind: Perception · System: Eyes & Vision, Brain
Also known as: Auditory-evoked phosphenes, Sound-induced phosphenes, Sound-induced photisms, Acquired auditory-visual synesthesia
Some people see a brief flash of light when they hear a sudden sound. Most published cases are people who have lost some vision. In one study, more than half of healthy students saw it after sitting in a dark room.
🏷️ try-it illusion sleep get-it-checked
Tetrachromacy ↗
Prevalence: About 12% of women carry a fourth cone type · Kind: Perception · System: Eyes & Vision, Whole Body & Genetics
Also known as: Four-cone colour vision, Functional tetrachromacy
Most people have three kinds of colour-sensing cone. About 12% of women carry a fourth. In theory they can tell apart colours that look identical to everyone else. Clear cases are extremely rare, and online tests cannot detect it.
🏷️ genetic debunked-myth
The blind spot ↗
Prevalence: Everyone · Kind: Perception · System: Eyes & Vision, Brain
Also known as: Physiological blind spot, Punctum caecum, Optic disc scotoma
Each eye has a hole in its field of view where the optic nerve leaves the retina. You never notice it, because the brain paints over the gap with whatever surrounds it.
🏷️ try-it illusion
Troxler effect ↗
Prevalence: Everyone · Kind: Perception · System: Eyes & Vision, Brain
Also known as: Troxler's fading, Troxler's effect
When you hold your gaze on one point, things in the edge of your vision fade out and disappear. The brain stops reporting anything that does not change.
🏷️ try-it illusion
Voluntary nystagmus ↗
Prevalence: About 8% of people · Kind: Trick · System: Eyes & Vision, Muscles & Tendons
Also known as: Eye shaking, Vibrating eyes, Eye wiggling
About 8% of people can make both eyes shake rapidly from side to side on command. It looks alarming and is harmless. It is tiring and lasts only seconds.
🏷️ try-it party-trick genetic
Voluntary pupil control ↗
Prevalence: One modern case study. No rate known · Kind: Trick · System: Eyes & Vision, Brain
Also known as: Direct pupil control, Conscious pupil dilation
Changing the size of your pupils by will alone, without imagining a light or doing sums. One case has been studied with modern methods. Older reports exist, but most describe indirect tricks. Indirect control by thinking hard is possible for almost everyone.
🏷️ try-it record
Wall-eyed divergence ↗
Prevalence: Not known · Kind: Trick · System: Eyes & Vision, Muscles & Tendons
Also known as: Voluntary divergence, Going wall-eyed
Turning both eyes outward, away from the nose, on purpose. Nobody has counted how many people can do it. Most people can learn the mild version, parallel viewing, from Magic Eye pictures.
🏷️ try-it learnable party-trick
Group 3: 👂 Ears & Hearing (14 oddities)
Auditory clicks, middle-ear muscle rumbles, phantom sounds, and anatomical traits.
Attached and free earlobes ↗
Prevalence: About 61% attached in one Korean sample · Kind: Variation · System: Ears & Hearing, Skin & Hair
Also known as: Earlobe attachment, Adherent earlobe
Some earlobes hang free and others join the head directly. Textbooks taught this as one gene, but a 2017 study found at least 49 genetic regions involved, and the two shapes blend into each other.
🏷️ debunked-myth genetic try-it
Autophony ↗
Prevalence: About 0.3–6.6% for patulous Eustachian tube · Kind: Sound · System: Ears & Hearing
Also known as: Hearing your own voice too loudly, Patulous Eustachian tube (a common cause)
Your own voice, breathing, or heartbeat sounds far too loud inside your head. It can mean a tube or a thin patch of bone is letting sound take a shortcut into the ear.
🏷️ get-it-checked
BPPV ↗
Prevalence: About 2.4% of people, lifetime · Kind: Involuntary · System: Ears & Hearing, Brain
Also known as: Benign paroxysmal positional vertigo, Positional vertigo, "Ear crystals"
A short, intense spinning feeling set off by turning over in bed or tipping your head back. Tiny crystals in the inner ear have drifted into the wrong place. It is the most common cause of vertigo and it is very treatable.
🏷️ get-it-checked
Darwin's tubercle ↗
Prevalence: 10–58% of people · Kind: Variation · System: Ears & Hearing
Also known as: Darwin's point, Auricular tubercle, Tuberculum auriculae
A small bump on the folded rim of the ear, which Darwin thought was the leftover tip of a pointed ancestral ear. Between 10% and 58% of people have one, depending on the population.
🏷️ vestigial try-it genetic
Ear clicking when swallowing ↗
Prevalence: Everyone · Kind: Sound · System: Ears & Hearing, Muscles & Tendons
Also known as: Eustachian tube click, Ear popping
Swallowing opens a small tube between your throat and your middle ear for a fraction of a second. The faint click you can hear is that tube letting air through to balance the pressure.
🏷️ try-it
Ear rumbling ↗
Prevalence: 43–55% of people · Kind: Trick · System: Ears & Hearing, Muscles & Tendons
Also known as: Voluntary tensor tympani contraction
Up to about half of all people can make a low roar inside their own head by tensing a tiny muscle in the middle ear.
🏷️ try-it community party-trick
Ear wiggling ↗
Prevalence: About 1 in 5 · Kind: Trick · System: Ears & Hearing, Muscles & Tendons
Also known as: Moving your ears, Auricular muscle control
Moving the outer ears using three small muscles that most mammals use to point their ears at sounds. About 1 in 5 people can wiggle their ears. Some people can learn.
🏷️ try-it learnable party-trick vestigial genetic
Preauricular pit ↗
Prevalence: 0.1–10% of people · Kind: Variation · System: Ears & Hearing, Skin & Hair
Also known as: Preauricular sinus, Ear pit, Congenital auricular fistula
A tiny hole in the skin just in front of the ear, present from birth, that can lead to a tunnel under the skin. It is harmless unless it gets infected.
🏷️ genetic get-it-checked
Pulsatile tinnitus ↗
Prevalence: Under 10% of people with tinnitus · Kind: Sound · System: Ears & Hearing, Heart & Blood
Also known as: Heartbeat in the ear, Vascular tinnitus
A whooshing or thumping in one ear that keeps time with your pulse. It is usually the sound of blood flowing near the ear. It often has a treatable cause, so get it checked.
🏷️ get-it-checked
Surfer's ear ↗
Prevalence: About 2 in 3 surfers · Kind: Variation · System: Ears & Hearing, Bones & Joints
Also known as: External auditory canal exostosis, Ear canal exostoses
Years of cold water and wind on the ear make small lumps of new bone grow inside the ear canal. About two in three surfers have some. Neanderthal skulls show it too, more often than those of early modern humans.
🏷️ get-it-checked
Tensor tympani thump ↗
Prevalence: Everyone · Kind: Sound · System: Ears & Hearing, Muscles & Tendons
Also known as: Yawn thump, Ear rumble when yawning, Tonic tensor tympani syndrome (when it spasms)
The low thump or rumble in your ears when you yawn or shout is a tiny middle ear muscle tensing to protect your hearing from your own noise.
The sound of silence ↗
Prevalence: 64–83% of people in studies · Kind: Sound · System: Ears & Hearing, Brain
Also known as: Anechoic chamber experience, Hearing your own body
In a room that absorbs almost all sound, many people hear their heartbeat, their blood, their breath, or a high ringing. True silence is not possible for a living person.
🏷️ debunked-myth record
Tinnitus ↗
Prevalence: About 10–15% of people · Kind: Involuntary · System: Ears & Hearing, Brain
Also known as: Ringing in the ears
A ringing, hissing, buzzing, or roaring sound with no source outside your head. Between 10% and 15% of people have it. It is mostly the hearing system filling in for damaged or tired inner-ear cells.
🏷️ get-it-checked community
Voluntary Eustachian tube opening ↗
Prevalence: No formal count · Kind: Trick · System: Ears & Hearing, Muscles & Tendons
Also known as: Béance tubaire volontaire, BTV, Voluntary tubal opening
Opening the tubes that link the middle ear to the throat on command, without swallowing or pinching your nose. You hear a click, and your own voice gets loud. Some divers and freedivers learn it, but most never do.
🏷️ try-it learnable
Group 4: 👄 Mouth & Throat (14 oddities)
Tongue mobility tricks, palate variations, taste perception, and airway reflexes.
Bifid uvula ↗
Prevalence: 1–2% of people · Kind: Variation · System: Mouth & Throat
Also known as: Uvula bifida, Split uvula, Cleft uvula
The uvula, the dangling flap at the back of the throat, is split into two lobes, in about 1 to 2% of people. On its own it is harmless, but in a baby it can be a clue to a hidden cleft of the palate.
🏷️ try-it get-it-checked genetic
Cloverleaf tongue ↗
Prevalence: About 15% (one Dutch sample) · Kind: Trick · System: Mouth & Throat, Muscles & Tendons
Also known as: Trefoil tongue, Three-leaf tongue
Folding the tongue into three lobes, like a clover leaf. In one Dutch study, about 15% of adults could do it. It is usually called the hardest tongue shape.
🏷️ try-it learnable party-trick genetic
Gag reflex ↗
Prevalence: Present in about 2 of 3 people, absent in 37% in one study · Kind: Reflex · System: Mouth & Throat, Nervous System & Reflexes
Also known as: Pharyngeal reflex
Touch the back of the tongue or the soft palate and the throat clamps shut. It keeps things out of the airway. About a third of healthy people have no gag reflex at all, and that is normal.
Geographic tongue ↗
Prevalence: 2–3% of people · Kind: Variation · System: Mouth & Throat
Also known as: Benign migratory glossitis, Wandering rash of the tongue
Smooth red patches with pale borders that form a map on the tongue and move around over days and weeks. About 2 to 3% of people have it, and it is harmless.
🏷️ not-an-emergency genetic
Gleeking ↗
Prevalence: No formal count · Kind: Trick · System: Mouth & Throat
Also known as: Saliva jet
Shooting a thin jet of saliva from under the tongue. It can happen by accident, often during a yawn, or on purpose. No survey has counted how many people can do it.
🏷️ icky try-it learnable party-trick
Gorlin's sign ↗
Prevalence: ~10% of people · Kind: Trick · System: Mouth & Throat, Whole Body & Genetics
Also known as: Gorlin sign, Touching your nose with your tongue
Touching the tip of your nose with your tongue. About 10% of people can do it. About half of people with Ehlers-Danlos syndrome can, so doctors use it as a quick check for stretchy connective tissue.
🏷️ try-it party-trick genetic icky
Inability to burp ↗
Prevalence: Unknown. Over 750 published cases · Kind: Involuntary · System: Mouth & Throat, Internal Organs & Digestion
Also known as: Retrograde cricopharyngeus dysfunction, R-CPD, No-burp syndrome, Abelchia
Some people have never been able to burp. A ring of muscle at the top of the food pipe does not open to let gas out, which causes gurgling, bloating and chest pressure. Doctors named it in 2019, after patients spread the word on Reddit.
🏷️ get-it-checked community
Pointed tongue ↗
Prevalence: ~55% · Kind: Trick · System: Mouth & Throat, Muscles & Tendons
Also known as: Tongue pointing
Making the tip of the tongue narrow and sharp, like a pencil point. About 55% of people in one Chinese survey can do it. It and tongue rolling are the two most common tongue tricks.
🏷️ try-it learnable party-trick
Supertasters ↗
Prevalence: About 25% of people · Kind: Variation · System: Mouth & Throat
Also known as: PROP supertaster
About a quarter of people taste bitter compounds far more strongly than everyone else. They tend to have more taste buds, and they often dislike coffee, dark greens, and grapefruit.
🏷️ genetic try-it
Tongue folding ↗
Prevalence: 1.5–27.5% · Kind: Trick · System: Mouth & Throat, Muscles & Tendons
Also known as: Inward tongue fold, Tongue flip
Folding the tip of the tongue backward over itself inside the mouth. Studies find that between 1.5% and 27.5% of people can do it.
🏷️ try-it learnable party-trick
Tongue rolling ↗
Prevalence: 65–84% of people · Kind: Trick · System: Mouth & Throat, Muscles & Tendons
Also known as: Tongue curling, U-shaped tongue
Between 65% and 84% of people can curl the sides of the tongue up into a tube. For decades it was taught as a simple one-gene trait. It is not.
🏷️ try-it learnable debunked-myth genetic
Tongue tie ↗
Prevalence: About 7% of babies · Kind: Variation · System: Mouth & Throat
Also known as: Ankyloglossia, Short frenulum
A short or tight band of tissue under the tongue that holds the tip down, present in about 1 in 14 babies. Some cannot breastfeed well, but many grow up with no trouble at all.
🏷️ childhood genetic
Tongue twisting ↗
Prevalence: 12–36% · Kind: Trick · System: Mouth & Throat, Muscles & Tendons
Also known as: Tongue turning, Tongue rotation
Turning the tongue on its side so the edges face up and down, or all the way over. Between 12% and 36% of people can twist it at least halfway.
🏷️ try-it party-trick
Tonsil stones ↗
Prevalence: Up to 10% of people; up to 46% on CT scans · Kind: Involuntary · System: Mouth & Throat
Also known as: Tonsilloliths, Tonsil calculi
Small white or yellow lumps that form in the folds of the tonsils and sometimes come out when you cough. They smell bad and feel like something is stuck in the throat. They are usually harmless.
🏷️ icky community not-an-emergency
Group 5: 👃 Nose & Olfaction (5 oddities)
Reflexive drips, flaring muscles, and olfactory variations.
Asparagus pee smell ↗
Prevalence: 6% to 60% cannot smell it, depending on the test · Kind: Variation · System: Nose & Olfaction, Internal Organs & Digestion
Also known as: Asparagus anosmia, Asparagus urine odour
After eating asparagus, many people notice a smell like cooked cabbage in their urine. Others never notice it. Two separate traits hide here. Some people do not make the smell, and some people cannot smell it.
🏷️ genetic icky try-it
Cilantro tastes like soap ↗
Prevalence: About 12% in one large survey · Kind: Variation · System: Nose & Olfaction, Mouth & Throat
Also known as: Coriander tastes like soap, Cilantro soapy-taste detection
In one large survey, about one person in eight said fresh cilantro tastes like soap. The difference is thought to lie mostly in smell, not taste. Genes play a part, but the one variant found so far explains very little of it.
🏷️ genetic try-it debunked-myth
Flaring your nostrils ↗
Prevalence: No formal count · Kind: Trick · System: Nose & Olfaction, Muscles & Tendons
Also known as: Nostril flaring, Alar flaring
Widening the nostrils on purpose. No study has counted how many people can do it on command. It also happens on its own during hard breathing and in strong emotion such as anger.
🏷️ try-it learnable party-trick
Photic sneeze reflex ↗
Prevalence: About 18–35% of people · Kind: Reflex · System: Nose & Olfaction, Eyes & Vision
Also known as: ACHOO syndrome, Sun sneezing, Autosomal dominant compelling helio-ophthalmic outburst
About one person in four sneezes when they step into bright sunlight. It runs in families, and the leading idea is a wiring mix-up between the nerve for the eyes and the nerve for the nose.
🏷️ genetic
Reflex runny nose ↗
Prevalence: About half of regular exercisers · Kind: Reflex · System: Nose & Olfaction, Nervous System & Reflexes
Also known as: Exercise-induced rhinitis, Skier's nose, Gustatory rhinitis
Exercise, cold air and hot or spicy food can all make a clear, watery drip run from the nose. It is mainly a nerve reflex, not a cold or an allergy. During exercise the nose even opens wider, yet in many people it still runs.
Group 6: 🧬 Skin & Hair (9 oddities)
Piloerection, tactile writing, dermatological traits, and water wrinkles.
Blushing ↗
Prevalence: Everyone · Kind: Reflex · System: Skin & Hair, Heart & Blood
Also known as: Erubescence, Erythema of embarrassment
When you are embarrassed, blood vessels in the face open wide and the skin turns red. You cannot stop it. Darwin called it the most human of all expressions, and no other animal is known to blush from embarrassment.
Dermatographia ↗
Prevalence: About 2–5% of people · Kind: Reflex · System: Skin & Hair
Also known as: Skin writing, Dermographism, Dermatographic urticaria
In a few people, a firm stroke on the skin raises a red welt within minutes, clear enough to write words with a fingernail. It is the skin's hive response set on a hair trigger.
🏷️ try-it
Double little toenail ↗
Prevalence: Over half of people in Chinese surveys · Kind: Variation · System: Skin & Hair
Also known as: Accessory nail of the fifth toe, Split pinky toenail, Petaloid toenail
A thin extra strip of nail on the outer edge of the little toenail. Surveys in China find it in over half of people. It is often called a Han Chinese trait, but it turns up in many populations.
🏷️ try-it debunked-myth genetic
Fordyce spots ↗
Prevalence: 70–80% of adults · Kind: Involuntary · System: Skin & Hair, Mouth & Throat
Also known as: Fordyce granules, Sebaceous prominence
Tiny pale yellow or white bumps, 1 to 3 mm across, on the edge of the lips or inside the cheeks. They are ordinary oil glands in a place without hair. Most adults have them.
🏷️ not-an-emergency
Goosebumps ↗
Prevalence: Everyone · Kind: Reflex · System: Skin & Hair, Muscles & Tendons
Also known as: Piloerection, Cutis anserina, Gooseflesh
Tiny muscles at the base of most hairs pull the hair upright when you are cold, scared, or moved. In a furry animal this traps warm air or makes it look bigger. In a human the raised hair does almost nothing.
🏷️ vestigial
Pruney fingers ↗
Prevalence: Nearly everyone with intact nerves · Kind: Involuntary · System: Skin & Hair, Nervous System & Reflexes
Also known as: Water-immersion wrinkling, Wrinkled fingertips
Fingertips and toes wrinkle after several minutes in water. This is not just the skin soaking up water. It is the nervous system shrinking the fingertip on purpose, and the wrinkles may improve grip when wet.
🏷️ debunked-myth try-it
Supernumerary nipples ↗
Prevalence: 0.2–5.6% of people · Kind: Variation · System: Skin & Hair, Whole Body & Genetics
Also known as: Third nipple, Polythelia, Accessory nipple
An extra nipple, usually small and flat, on a line running from the armpit to the groin. Between 1 in 500 and 1 in 18 people have one, and it is often mistaken for a mole.
🏷️ genetic famous-people not-an-emergency
Sweaty palms ↗
Prevalence: Not counted · Kind: Reflex · System: Skin & Hair, Brain
Also known as: Emotional sweating, Psychological sweating
A video of someone climbing a crane with no rope can make your own palms wet, even if you are not afraid of heights. Fear and stress switch on the sweat glands of the palms and soles. It is the same signal a lie detector reads.
🏷️ try-it community
Voluntary piloerection ↗
Prevalence: Unknown, but rare · Kind: Trick · System: Skin & Hair, Nervous System & Reflexes
Also known as: Voluntary goosebumps, VGP
Giving yourself goosebumps on command, without music, cold, or fear. Nobody knows how many people can do it, but it seems rare. The muscles involved are not supposed to take orders.
🏷️ try-it community
Group 7: 💪 Muscles & Tendons (8 oddities)
Vestigial tendons, involuntary twitches, and voluntary muscle control.
Benign fasciculations ↗
Prevalence: About 70% of clinicians in one survey · Kind: Involuntary · System: Muscles & Tendons, Nervous System & Reflexes
Also known as: Muscle twitches, Benign fasciculation syndrome, BFS
Small visible twitches in the eyelid, calf, thumb, or arm that come and go with no weakness. One survey found them in about 70% of healthy clinicians. They are very rarely a sign of nerve disease.
🏷️ not-an-emergency community
Diastasis recti ↗
Prevalence: Almost all first pregnancies; about 1 in 3 women a year after birth · Kind: Variation · System: Muscles & Tendons, Whole Body & Genetics
Also known as: Abdominal separation, Divarication of the recti, Mummy tummy
A widening of the gap between the two halves of the six-pack muscle, seen in nearly every first pregnancy and in some men. A bulge down the midline when you sit up is the usual sign.
🏷️ try-it not-an-emergency
Linburg–Comstock variation ↗
Prevalence: About 1 in 5 people. Studies range from 5% to 60%. · Kind: Variation · System: Muscles & Tendons
Also known as: Linburg–Comstock syndrome, Linburg–Comstock anomaly, Linked thumb and index finger tendons
An extra tendon link in the forearm that ties the thumb to the index finger. When the thumb bends into the palm, the index fingertip bends with it. Roughly 1 in 5 people have it, but counts vary widely.
🏷️ try-it vestigial
Palmaris longus ↗
Prevalence: Missing in about 15–20% of people · Kind: Variation · System: Muscles & Tendons
Also known as: Missing forearm tendon, Palmaris longus agenesis
A thin tendon that stands out in the wrist when you press your thumb and little finger together. About 1 in 7 people do not have it at all, and they lose nothing.
🏷️ try-it vestigial genetic
Plantaris muscle ↗
Prevalence: Missing in 7–20% of people · Kind: Variation · System: Muscles & Tendons
Also known as: Freshman's nerve
A small calf muscle with a very long, thin tendon that medical students mistake for a nerve. Between 7% and 20% of people do not have it.
🏷️ vestigial
Platysma display ↗
Prevalence: No formal count · Kind: Trick · System: Muscles & Tendons
Also known as: Neck flexing, Neck cords
Tensing the thin sheet of muscle under the skin of the neck so that cords stand out from jaw to collarbone. Everyone has the muscle. Nobody has counted how many can flex it on its own.
🏷️ try-it learnable party-trick
Proctalgia fugax ↗
Prevalence: About 7% of adults. Studies range from 4% to 18%. · Kind: Involuntary · System: Muscles & Tendons, Internal Organs & Digestion
A sudden, cramping pain deep in the rectum that lasts seconds to minutes and then goes away completely. It has no known cause, and it is harmless.
🏷️ not-an-emergency
Raising one eyebrow ↗
Prevalence: 30–40% (informal estimate) · Kind: Trick · System: Muscles & Tendons, Skin & Hair
Also known as: The People's Eyebrow, Single eyebrow raise
Lifting a single eyebrow while the other stays down. A popular science magazine puts it at 30% to 40% of people, but no study has measured it.
🏷️ try-it learnable party-trick famous-people
Group 8: 🦴 Bones & Joints (13 oddities)
Hypermobility, accessory bones, joint cavitation, and skeletal variations.
Accessory ossicles ↗
Prevalence: About 2 in 5 feet · Kind: Variation · System: Bones & Joints
Also known as: Extra bones, Accessory bones
Small extra bones, most often in the foot, that form when a growth centre never fuses with its main bone. They are usually harmless but can be mistaken for fractures on an X-ray.
🏷️ not-an-emergency
Camptodactyly ↗
Prevalence: Under 1% of people · Kind: Variation · System: Bones & Joints
Also known as: Flexed little finger, Flexion contracture of the little finger
A finger that stays bent forward at its middle joint and cannot fully straighten, usually the little finger. Under 1% of people have it. Mild cases rarely cause trouble, but the bend can get worse while a child grows.
🏷️ genetic get-it-checked try-it
Cervical rib ↗
Prevalence: About 1% of people · Kind: Variation · System: Bones & Joints, Nervous System & Reflexes
Also known as: Neck rib, Extra rib
An extra rib above the normal top rib, growing from the lowest bone in the neck. About 1 in 100 people have one, and most never know.
🏷️ not-an-emergency genetic
Clinodactyly ↗
Prevalence: 1–20% of people · Kind: Variation · System: Bones & Joints
Also known as: Curved little finger, Bent pinky
A finger that curves sideways toward its neighbours, most often the little finger leaning toward the ring finger. Between 1% and 20% of people have it, and on its own it is harmless.
🏷️ try-it genetic
Hitchhiker's thumb ↗
Prevalence: 24–36% of people in the US · Kind: Variation · System: Bones & Joints
Also known as: Distal hyperextensibility of the thumb, Bendy thumb
A thumb whose top joint bends back past 50 degrees, once taught as a simple recessive gene. Thumb angle is really a smooth range, and the genetics are not that simple.
🏷️ try-it debunked-myth genetic
Joint hypermobility ↗
Prevalence: 10–25% of people · Kind: Variation · System: Bones & Joints, Whole Body & Genetics
Also known as: Double-jointedness, Generalised joint hypermobility
About 1 in 5 people have joints that bend further than usual, measured with a nine-point test called the Beighton score. For most people it causes no trouble.
🏷️ try-it get-it-checked genetic party-trick
Knuckle cracking ↗
Prevalence: 25–54% crack habitually · Kind: Trick · System: Bones & Joints
Also known as: Joint cracking, Crepitus, Joint cavitation
Pulling or bending a finger joint until it pops. Between 25% and 54% of people do it out of habit. The pop comes from a gas bubble in the joint fluid, and it does not cause arthritis.
🏷️ try-it debunked-myth record
Midtarsal break ↗
Prevalence: About 1 in 12 (8%) · Kind: Trick · System: Bones & Joints, Whole Body & Genetics
Also known as: Flexible midfoot, Bendy feet, Midfoot break
A foot that bends in the middle, between the heel and the ball, as well as at the toes. About 1 in 12 people have it. It looks like the midfoot bend of apes.
🏷️ try-it
Morton's toe ↗
Prevalence: 3–22% of people · Kind: Variation · System: Bones & Joints
Also known as: Greek foot, Royal toe, Long second toe, Morton's foot
A second toe that looks longer than the big toe because the first metatarsal bone in the foot is short. It is common, and it is the foot shape seen on classical Greek statues.
🏷️ try-it genetic
Sixth lumbar vertebra ↗
Prevalence: Roughly 1 in 20 people · Kind: Variation · System: Bones & Joints
Also known as: Lumbosacral transitional vertebra, Lumbarization, Sacralization
Most people have five bones in the lower back. Roughly 1 in 20 have six. Most never find out unless a scan shows it, and the extra bone can confuse doctors who count vertebrae to find the right level.
🏷️ not-an-emergency
Torus palatinus ↗
Prevalence: About 20% of people · Kind: Variation · System: Bones & Joints, Mouth & Throat
Also known as: Palatal torus, Bony bump on the roof of the mouth
A hard bony lump along the midline of the roof of the mouth that grows slowly and is completely harmless. Many people find it by chance and worry that it is a tumour. A similar bump inside the lower jaw is a torus mandibularis.
🏷️ not-an-emergency try-it genetic
Voluntary joint dislocation ↗
Prevalence: 0.5–2.6% (shoulder, one survey) · Kind: Trick · System: Bones & Joints, Whole Body & Genetics
Also known as: Voluntary subluxation, Popping joints out
Pushing a joint partly or fully out of its socket on purpose, then back in. Between 10% and 25% of people have some joint hypermobility. One survey of students and their siblings found 0.5% to 2.6% could dislocate a shoulder at will.
🏷️ icky get-it-checked genetic party-trick
Webbed toes ↗
Prevalence: About 1 in 2,000–2,500 births · Kind: Variation · System: Bones & Joints, Skin & Hair
Also known as: Syndactyly of the toes, Zygodactyly, Partial syndactyly
Two toes joined by skin, most often the second and third, in about 1 in 2,000 to 2,500 babies. The toes usually work normally and many people leave them as they are.
🏷️ genetic famous-people
Group 9: 🫀 Heart & Blood (5 oddities)
Vascular reflexes, blood shifting, syncope, and cardiac control.
Diving reflex ↗
Prevalence: Everyone · Kind: Reflex · System: Heart & Blood, Nervous System & Reflexes
Also known as: Mammalian diving reflex, Diving response
Cold water on the face makes the heart slow down, sends blood to the brain, and holds the breath. Every mammal studied so far has it. You can trigger it with a bowl of cold water.
🏷️ try-it
Heart rate control ↗
Prevalence: No formal count · Kind: Trick · System: Heart & Blood, Brain
Also known as: Volitional heart rate control, Cardiac biofeedback
Slowing or speeding up your own heartbeat on purpose, using breath, attention, or training. Breathing can shift it a little within minutes. A few trained people shift it a lot.
🏷️ spiritual learnable try-it
Oculocardiac reflex ↗
Prevalence: Found in 14–90% of eye muscle operations. Its strength varies a lot. · Kind: Reflex · System: Heart & Blood, Eyes & Vision
Also known as: Aschner reflex, Aschner–Dagnini reflex, Trigeminovagal reflex
Pressure on the eyeball, or a pull on an eye muscle, makes the heart slow down. It matters most during eye surgery, especially in children. It is not a safe way to slow your own heart.
Seeing stars when standing up ↗
Prevalence: Almost everyone, at some time · Kind: Involuntary · System: Heart & Blood, Eyes & Vision
Also known as: Postural hypotension, Orthostatic hypotension, Head rush
You stand up fast, your vision goes grey or sparkly, and your head feels light for a few seconds. Blood has briefly pooled in your legs. It passes on its own.
🏷️ not-an-emergency
Vasovagal syncope ↗
Prevalence: About 1 in 3 people faint at least once · Kind: Reflex · System: Heart & Blood, Nervous System & Reflexes
Also known as: Vasovagal response, Reflex syncope, Common faint
The most common reason people faint. A trigger like blood, pain, heat, or standing too long makes the vagus nerve slow the heart, and blood pressure drops. The brain briefly runs short of blood and you go down.
🏷️ get-it-checked
Group 10: 🫁 Internal Organs & Digestion (6 oddities)
Gastrointestinal sounds, kidney diuresis, diaphragm spasms, and visceral mechanics.
Cold diuresis ↗
Prevalence: Everyone · Kind: Reflex · System: Internal Organs & Digestion, Heart & Blood
Also known as: Cold-induced diuresis, Needing to pee when cold
Being cold makes you need to urinate. The body pulls blood away from the skin into the core, the heart reads this as too much blood, and the kidneys are told to dump water.
Extraordinary breath-holding ↗
Prevalence: Trained divers only; no count · Kind: Rare Ability · System: Internal Organs & Digestion, Heart & Blood
Also known as: Static apnea
Untrained adults usually stop within a minute or two. The best freedivers manage over 11 minutes, and over 29 minutes after breathing pure oxygen. One group of sea nomads has evolved larger spleens for diving.
🏷️ learnable record
Hiccups ↗
Prevalence: Everyone · Kind: Sound · System: Internal Organs & Digestion
Also known as: Singultus, Hiccoughs
A hiccup is a sudden jerk of the diaphragm followed by the voice box snapping shut. Everyone gets them, even before birth. The record case lasted 68 years.
🏷️ vestigial record
Immersion diuresis ↗
Prevalence: A normal body response · Kind: Reflex · System: Internal Organs & Digestion, Heart & Blood
Also known as: Needing to pee in water, Needing to pee in the bath or pool
Sitting in water up to your neck makes the kidneys produce extra urine. The main cause is water pressure, not cold. Body-warm water works as well as cool water, and in one study the warmest water had the smallest effect.
🏷️ debunked-myth try-it
Stomach growling ↗
Prevalence: Everyone · Kind: Sound · System: Internal Organs & Digestion
Also known as: Borborygmi, Stomach rumbling, Bowel sounds
The rumble from your belly is gas and liquid being pushed through your gut by waves of muscle. It is louder when you are hungry because there is less food to muffle it.
Voluntary burping ↗
Prevalence: No formal count · Kind: Trick · System: Internal Organs & Digestion, Mouth & Throat
Also known as: Burping on command, Voluntary eructation
Swallowing air on purpose and letting it back up as a belch. Nobody has counted how many people can do it. The loudest recorded burp reached 112.4 decibels.
🏷️ try-it learnable party-trick record
Group 11: ⚡ Nervous System & Reflexes (12 oddities)
Primitive reflexes, sensory misdirection, and neural wiring quirks.
Babinski reflex ↗
Prevalence: Most healthy newborns · Kind: Reflex · System: Nervous System & Reflexes
Also known as: Babinski sign, Extensor plantar response
Stroke the sole of a baby's foot and the big toe lifts while the other toes fan out. Do the same to an adult and the toes curl down. The baby's response is normal until about two years. In an adult it is a warning sign.
🏷️ childhood
Brain freeze ↗
Prevalence: About 40–50% of people · Kind: Involuntary · System: Nervous System & Reflexes, Mouth & Throat
Also known as: Cold-stimulus headache, Ice cream headache, Sphenopalatine ganglioneuralgia
A short, sharp headache in the forehead a few seconds after cold food or drink touches the roof of the mouth. It usually passes in under a minute.
🏷️ try-it
Congenital insensitivity to pain ↗
Prevalence: About 1 in 1,000,000 · Kind: Rare Ability · System: Nervous System & Reflexes, Whole Body & Genetics
Also known as: CIP, Congenital analgesia
A tiny number of people are born unable to feel pain. Single-gene changes switch off their pain nerves. It is not a superpower. Injuries go unnoticed, and most people with it are badly hurt in childhood.
🏷️ genetic
Cutaneous rabbit illusion ↗
Prevalence: Felt on 90% of trials in one brain-scan study · Kind: Reflex · System: Nervous System & Reflexes, Brain
Also known as: Sensory saltation, The cutaneous rabbit
A few quick taps at the wrist followed by taps at the elbow feel like a small animal hopping up the arm. The brain fills in taps between the two spots that never happened.
🏷️ illusion
Knee-jerk reflex ↗
Prevalence: Everyone · Kind: Reflex · System: Nervous System & Reflexes, Muscles & Tendons
Also known as: Patellar reflex, Patellar tendon reflex
A tap on the tendon below the kneecap makes the lower leg kick. The signal goes to the spinal cord and straight back through one connection. It is a classic example of a one-synapse reflex.
🏷️ try-it
Palmar grasp reflex ↗
Prevalence: All healthy newborns · Kind: Reflex · System: Nervous System & Reflexes, Muscles & Tendons
Also known as: Grasp reflex, Darwinian reflex
Put a finger in a newborn's palm and the fingers close around it, hard. The grip is strong enough to hold the baby's weight for a moment. It fades by about six months and is replaced by grasping on purpose.
🏷️ childhood
Pee shivers ↗
Prevalence: Nobody has counted it · Kind: Involuntary · System: Nervous System & Reflexes, Internal Organs & Digestion
Also known as: Post-micturition convulsion syndrome, Piss shivers
A brief involuntary shudder during or just after urinating. Many people seem to get it, men more often than women. It is widely known and almost completely unstudied.
Pinocchio illusion ↗
Prevalence: About 30% of students in one lab test · Kind: Perception · System: Nervous System & Reflexes, Brain
Also known as: Phantom nose illusion
Vibrate the biceps tendon while a person touches their own nose with their eyes closed, and their nose can feel as if it is growing. It shows how the brain works out where the body parts are.
🏷️ illusion
Pins and needles ↗
Prevalence: Everyone · Kind: Involuntary · System: Nervous System & Reflexes
Also known as: Transient paresthesia, "My foot fell asleep"
The prickling, buzzing feeling in a limb after you sit on it or lean on it. It happens when blood returns to a squeezed nerve and its sensory fibres briefly fire on their own.
🏷️ try-it
Precordial catch syndrome ↗
Prevalence: 80–90% of chest pain in young people, once injury is ruled out · Kind: Involuntary · System: Nervous System & Reflexes, Heart & Blood
Also known as: Texidor's twinge
A sudden, sharp, stabbing pain near the heart that lasts seconds to a few minutes and gets worse when you breathe in. Doctors count it among the most common causes of chest pain in children and teenagers, and it is harmless.
🏷️ not-an-emergency childhood
Random shivers ↗
Prevalence: Not known · Kind: Involuntary · System: Nervous System & Reflexes, Muscles & Tendons
Also known as: Shudder, "Someone walked over my grave"
A single brief shudder that runs down the spine or through the whole body when you are not cold. Many people report them. Nobody has counted them.
Referred pain ↗
Prevalence: Everyone · Kind: Reflex · System: Nervous System & Reflexes
Also known as: Reflective pain
Pain from an internal organ often shows up somewhere else, like the left arm during a heart attack or the shoulder blade from a gallbladder. The nerves from the organ and from that patch of skin share a line into the spinal cord.
Group 12: 🧍 Whole Body & Genetics (3 oddities)
Systemic genetic variations, chimerism, mirror anatomy, and rare physiological traits.
CCR5-delta32 ↗
Prevalence: About 1% of Northern Europeans (two copies) · Kind: Rare Ability · System: Whole Body & Genetics, Heart & Blood
Also known as: CCR5-Δ32, CCR5 delta 32 deletion
About 1% of people of Northern European descent carry two copies of a broken gene that makes them almost immune to the most common form of HIV. A bone marrow transplant from one such donor produced the first cure of HIV.
🏷️ genetic famous-people
Chimerism ↗
Prevalence: Unknown. Fewer than 100 documented cases · Kind: Rare Ability · System: Whole Body & Genetics
Also known as: Tetragametic chimerism, Human chimera
A chimera is one person made of two sets of cells with different DNA. It can happen when two embryos fuse in the first days of pregnancy. Most chimeras never find out. A few discovered it when a DNA test said they were not the mother of their own children.
🏷️ famous-people genetic
Situs inversus ↗
Prevalence: About 1 in 10,000 people · Kind: Variation · System: Whole Body & Genetics, Internal Organs & Digestion
Also known as: Situs inversus totalis, Mirror-image organs
All the organs in the chest and belly sit on the opposite side from usual, as in a mirror. About 1 in 10,000 people are built this way, and most are healthy.
🏷️ genetic famous-people