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%
Muscle
Muscles under unusual control, muscles that twitch, and muscles some people do not have.
27 oddities. 7 have this as their primary region.
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.
About 70% of healthy people
Mouth Trick
Cloverleaf tongue
Folding the tongue into three lobes, like a clover leaf. Between 10% and 15% of people in Western samples can do it. It is usually called the hardest tongue shape.
10–15% (Western samples)
Eyes Trick
Crossing your eyes
Turning both eyes inward toward the nose on purpose. Nearly everyone with normal two-eyed vision can do it. Your eyes will not get stuck that way.
Nearly everyone
Muscle Variation
Diastasis recti
A widening of the gap between the two halves of the six-pack muscle, seen in nearly every pregnancy and in some men. A bulge down the midline when you sit up is the usual sign.
Almost all pregnancies; about 1 in 3 women a year after birth
Ears Sound
Ear clicking when swallowing
Every swallow 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.
Everyone
Ears Trick
Ear rumbling
About half of all people can make a low roar inside their own head by tensing a tiny muscle in the middle ear.
43–55% of people
Ears Trick
Ear wiggling
Moving the outer ears using three small muscles that most mammals use to point their ears at sounds. Between 10% and 22% of people can wiggle at least one ear. Many more can learn.
10–22% (one ear)
Muscle Trick
Flaring your nostrils
Widening the nostrils on purpose. About 30% of people can do it on command. Everyone does it without thinking during hard breathing and strong emotion.
~30% on command
Skin Reflex
Goosebumps
Tiny muscles at the base of every hair 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 it does almost nothing.
Everyone
Brain Involuntary
Hypnic jerks
A sudden jolt of the arms, legs, or whole body just as you fall asleep, often with a feeling of falling. Most people get them, and they are harmless.
60–70% of people
Nerves Reflex
Knee-jerk 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 the simplest reflex in the body.
Everyone
Nerves Reflex
Palmar grasp 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.
All healthy newborns
Muscle Variation
Palmaris longus
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.
Missing in about 15% of people
Muscle Variation
Plantaris muscle
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.
Missing in 7–20% of people
Muscle Trick
Platysma display
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. Isolated control of it is uncommon.
No formal count
Mouth Trick
Pointed tongue
Making the tip of the tongue narrow and sharp, like a pencil point. About 55% of people can do it. After rolling, it is the most common tongue trick.
~55%
Muscle Trick
Raising one eyebrow
Lifting a single eyebrow while the other stays down. Between 30% and 35% of people can do it without training. Most of the rest can learn it in front of a mirror.
30–35%
Nerves Involuntary
Random shivers
A single brief shudder that runs down the spine or through the whole body when you are not cold. It is very common, and nobody has studied it formally.
Very common, no formal count
Brain Involuntary
Sleep paralysis
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.
8–30% of people, lifetime
Ears Sound
Tensor tympani thump
The low thump or rumble in your ears when you yawn, cough, or shout is a tiny middle ear muscle tensing to protect your hearing from your own noise.
Everyone
Mouth Trick
Tongue folding
Folding the tip of the tongue backward over itself inside the mouth. Between 14% and 27.5% of people can do it.
14–27.5%
Mouth Trick
Tongue rolling
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.
65–84% of people
Mouth Trick
Tongue twisting
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.
12–36%
Ears Trick
Voluntary Eustachian tube 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. Divers and frequent flyers learn it.
Many can learn it; no formal count
Eyes Trick
Voluntary nystagmus
Between 5% and 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.
5–8% of people
Eyes Trick
Wall-eyed divergence
Turning both eyes outward, away from the nose, on purpose. It is much rarer than crossing the eyes. Most people can learn a mild version through Magic Eye pictures.
Rarer than crossing; no formal count