Browse by body region Browse by kind Recently added Changelog Brain Involuntary ASMR 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.

Unclear; estimates 20–70% Muscle Involuntary Benign fasciculations Small visible twitches in the eyelid, calf, thumb, or arm that come and go with no weakness. About 70% of healthy people get them. They are not a sign of nerve disease.

Ears Involuntary BPPV 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.

About 2.4% of people, lifetime Nerves Involuntary Brain freeze A short, sharp headache in the forehead a few seconds after cold food or drink touches the roof of the mouth. It passes in under a minute. About 30–40% of people Brain Involuntary Brain zaps 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 not dangerous. 15–50% of people stopping an antidepressant get withdrawal symptoms Brain Involuntary Call of the void A sudden, brief thought of jumping when you stand somewhere high, or of swerving while driving, with no wish to do it. About half of people get it.

It is the brain's safety system being misread, not a hidden wish. 43–60% of people Try one right now See all Each of these takes under a minute and needs nothing but your own body. Eyes Perception Afterimages 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. Everyone Brain Trick Ambidexterity Using both hands equally well for every task. Fewer than 1% of people are truly ambidextrous.

Most people who say they are ambidextrous are mixed-handed: right hand for some jobs, left for others. Under 1% Ears Variation Attached and free earlobes 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.

About 61% attached in one Korean sample Mouth Variation Bifid 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. 1–2% of people Eyes Perception Blue arcs of the retina Look at a small red light in a dark room and two faint blue arcs curve away from it towards your blind spot. You are seeing the nerve fibres of your own retina light up. 94% of healthy eyes in one clinic test Eyes Perception Blue field entoptic phenomenon 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. Everyone It felt scary but it is normal See all Things that alarm people and turn out to be harmless. Each entry says when a doctor is still a good idea.

Bones Variation Accessory ossicles Small extra bones, most often in the foot, that form when a growth centre never fuses with its main bone. They are harmless but can be mistaken for fractures on an X-ray. Up to 1 in 5 feet Brain Perception Alice in Wonderland syndrome 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 usually linked to migraine. 6–7% of teenagers (size distortion) Bones Variation Cervical 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.

About 1% of people Brain Per...