50 Fun Facts About The Five Senses

Which stirrup-shaped bone of the middle ear is the smallest and lightest bone in the human body?

The stapes takes its name from the Medieval Latin for stirrup. Classical Latin had no such word, because stirrups did not exist in the ancient world.

Which raised-dot system, devised by a blind French teenager, lets people read with their fingertips?

Braille began as an improvement on night writing, a tactile code built from 12-dot cells. Louis Braille, aged fifteen, cut each cell down to six dots.

Which chirping insects listen to one another's songs through hearing organs set in their front legs?

Crickets hear through thin membranes on the shins of their front legs. Only the males sing, and they do it by scraping their leathery front wings together.

Which leafy herb tastes like soap to some people because of a variant in a smell-receptor gene?

Cilantro divides diners because of the gene OR6A2, which builds a smell receptor: people with certain variants perceive the leaves as soapy or rotten.

Which lizard can swivel each eye independently, watching two different objects at the same time?

Chameleon eyelids are joined, leaving only a pinhole to see through. When prey appears, both eyes swing forward to lock onto the same target.

Which fifth basic taste did the Japanese chemist Kikunae Ikeda identify while studying kelp broth?

Umami is the meaty depth of parmesan, soy sauce and ripe tomatoes. Ikeda traced it to glutamate, and within a year the seasoning MSG was on sale in Japan.

Which German composer, almost deaf in later life, had visitors write their remarks in notebooks?

Ludwig van Beethoven was almost completely deaf when he wrote his Ninth Symphony. At its premiere a singer had to turn him around to see the applause.

The coloured ring of the human eye shares its name with which Greek goddess of the rainbow?

Iris suits the part because of the many colours it can take, yet one dark pigment, melanin, lies behind every normal shade from brown to blue.

Which sense depends on three fluid-filled looping canals that sit beside the hearing organ in the inner ear?

Balance relies on the semicircular canals, which stand at right angles to one another so that a head turn in any direction stirs the fluid in at least one.

Which birds make up for eyes fixed in their sockets by turning their heads as much as 270 degrees?

Owls back up that fixed stare with sharp hearing. In many species the ear openings are placed asymmetrically, which helps them judge where a sound is coming from.

Which American author, blind and deaf from infancy, learned language from words spelled into her hand?

Helen Keller made her breakthrough when her teacher spelled a word on one palm while running cool water over the other. She later earned a college degree.

Which kitchen vegetable releases a gas when it is chopped that stings the eyes and brings on tears?

Onion cells release a gas, syn-propanethial-S-oxide, when they are cut. It activates nerves in the eye, and the tear glands respond by trying to flush it out.

Which two colours are hardest to tell apart in the commonest inherited form of colour blindness?

Red and green confusion affects up to 1 in 12 males but only about 1 in 200 females, because the genes involved sit on the X chromosome.

Which nutrient, made by the body from the carotene in carrots, does the eye need to see in dim light?

Vitamin A is built into rhodopsin, the light-absorbing pigment of the eye, which is why one of the first signs of running short is night blindness.

Which ability lets dolphins and bats find prey in darkness by listening for their own calls bouncing back?

Echolocation was a mystery when Lazzaro Spallanzani showed in the 1790s that blinded bats still steer around obstacles. The word itself was coined only in 1944, by the zoologist Donald Griffin.

Which mammal hunts underwater with its eyes, ears and nostrils shut, sensing the electric fields of its prey?

The platypus has about 40,000 electroreceptors arranged in rows along its bill, picking up the tiny currents made when a prey animal's muscles contract.

Which radiation, invisible to humans, lets honey bees see guiding patterns on some flower petals?

Ultraviolet markings called nectar guides point pollinators towards a flower's centre, and the hidden colour bees see there has been nicknamed bee violet.

Which dark opening in the centre of the eye widens in dim light and shrinks in bright sunshine?

The pupil looks black because light entering it is absorbed by the tissues inside the eye, so almost none finds its way back out.

Which fish has taste sensors spread across its entire body, especially on the barbels around its mouth?

Catfish have chemoreceptors across their whole bodies, so they taste anything they touch and can sniff out chemicals drifting through the water.

Which watery fluid must first carry the chemicals in food to the taste buds before they can be detected?

Saliva is the liquid that ferries food chemicals to the taste receptor cells, which is why people who make too little of it can find their sense of taste dulled.

Which light-sensitive layer lining the back of the eye does the same job as the sensor in a camera?

The retina takes its name from the Latin rete, meaning net. Herophilos, who identified it around 300 BCE, thought the layer resembled a casting net.

Which spiral chamber of the inner ear takes its name from the Greek word for snail?

The cochlea makes two and three-quarter turns in humans. Egg-laying mammals such as the echidna are the exception among mammals, with one that is not coiled.

Which condition makes one sense trigger another, so that a person might taste words or see sounds as colours?

Synesthesia comes from the Greek for 'together' and 'sensation'. In one of its most common forms, each letter of the alphabet seems tinged with its own colour.

Which Greek philosopher gave sight, sound, smell, taste and touch a chapter each in his treatise On the Soul?

Aristotle argued that touch is the one sense every animal has, and that sight, hearing and the others all presuppose it.

Which compound from mint plants feels cool because it chemically triggers the body's cold-sensing receptors?

Menthol does not actually cool anything. It switches on TRPM8, the receptor that real cold activates, so the nerves report a chill that is not there.

Which chemical gives chilli peppers their burn in mammals yet goes unfelt by the birds that spread the seeds?

Capsaicin binds the same receptor that scalding heat sets off, so the burn is a false alarm. Work on that receptor shared the 2021 Nobel Prize in medicine.

Which condition, named from the Latin for 'to ring', makes a person hear sounds that have no outside source?

Tinnitus is most often caused by hearing damage. No drug treats it, though sound generators and hearing aids may help.

What name is given to the feeling, reported by most amputees, that a missing arm or leg is still attached?

Phantom limb was coined in the 1870s by the physician Silas Weir Mitchell, who likened the lingering presence to a ghost. Between 50 and 80 percent of amputees feel one.

Which sense of body position, checked in police sobriety tests, lets you touch your nose with eyes closed?

Proprioception is dulled by alcohol, which is why the test works: a sober person misses their own nose by no more than about 20 millimetres.

Which light receptors at the back of the eye work in daylight and let people see colour?

Cone cells come in three kinds in most people, each tuned to different wavelengths. Rods take over in dim light and play little part in colour, which is why colours fade at dusk.

Which sea animal has no blind spot, because its optic nerve fibres reach the light receptors from behind?

The octopus eye evolved independently of ours. In every vertebrate the nerve has to pass through the light-detecting layer, leaving a gap that the brain fills in.

Which eye condition dimmed the sight of the painter Claude Monet until he finally agreed to an operation?

Cataracts are a clouding of the eye's natural lens. While Monet had them his brushstrokes grew broader and his paintings darker, and at first he rejected surgery.

What is the medical term for losing the ability to smell, which became known as a common symptom of COVID-19?

Anosmia proved a better predictor of COVID-19 than fever or cough in a survey of two million people in the UK and US.

What name did two Australian researchers coin for the earthy scent of rain falling on dry soil?

Petrichor joins the Greek for stone with ichor, the fluid in the veins of the gods. The human nose can pick up one of its ingredients at 0.4 parts per billion.

Which thin membrane between the outer ear and the middle ear vibrates when sound waves strike it?

The eardrum is shaped like a shallow funnel, not flat. A small bone called the malleus is fixed to its inner face and passes each vibration along the chain.

Which dog breed, with nearly 300 million scent receptors, has tracked people since the Middle Ages?

The bloodhound follows a human trail so well that its identification of a suspect is accepted as evidence in some courts.

Which land animals keep in touch over long distances using rumbles pitched too low for people to hear?

Elephants produce infrasonic rumbles, and they also communicate with seismic signals, vibrations that travel through the ground itself.

Which cranial nerve, the shortest of the twelve, carries scent signals from the nose towards the brain?

The olfactory nerve is unusual among cranial nerves because it can regrow to some extent after damage. Its fibres reach the brain through a sieve-like plate of bone.

Which sound sensors of the inner ear can never grow back in humans once they are damaged?

Hair cells are named for the tuft of fine bristles on top of each one. Birds and zebrafish can regrow theirs, but in humans the loss is permanent.

What are the small bumps covering the upper surface of the tongue, some of which house taste buds, called?

Papillae come in four types on the human tongue. The most numerous kind carry no taste buds at all, and in cats they are tough enough to make the tongue rough.

Which structure in the roof of a snake's mouth analyses the scent particles gathered by its forked tongue?

Jacobson's organ takes its name from the anatomist who described it in 1813. The fork in the tongue gives a snake directional information about where a scent is coming from.

Which relay station deep in the brain handles incoming signals from every sense except smell?

The thalamus has a dedicated nucleus for each of the other senses, receiving their signals and sending them on to the matching area of the cortex.

What do neuroscientists call the brain's distorted body map, drawn with huge hands, lips and face?

The homunculus, Latin for little man, was devised by the neurosurgeon Wilder Penfield. Its hands are huge because so much of the brain handles their signals.

Which illusion, reported in the paper 'Hearing Lips and Seeing Voices', shows that lip movements alter what is heard?

The McGurk effect pairs the sound of one syllable with lip movements for another, and listeners often perceive a third sound that was never spoken.

Which reflective layer behind the eye's light receptors makes the eyes of cats shine in the dark?

The tapetum lucidum of cats shines so brightly that ancient Egyptians believed it reflected the sun at night. Humans have no such layer.

Which French novelist gave his name to taste-triggered memories after describing a tea-soaked madeleine?

Marcel Proust called such recollections involuntary memories. In his novel a bite of the cake restores a long-forgotten childhood scene with the narrator's aunt.

Which burrowing animal uses 22 fleshy appendages on its face to find and eat prey faster than any other mammal?

The star-nosed mole packs more than 25,000 touch receptors into a nose about 1.5 cm across, and can identify and swallow a morsel in as little as 120 milliseconds.

Which theory of pain, put forward by Ronald Melzack and Patrick Wall, explains why rubbing a bump eases the hurt?

Gate control holds that harmless input, such as the feel of rubbing, closes a nerve gate to pain signals before they reach the brain. It also gave a physical explanation for the way state of mind alters pain.

Which age-related loss of close focus, common after forty, takes its name from the Greek for 'old' and 'sight'?

Presbyopia has a different cause from ordinary far-sightedness: the lens of the eye stiffens with age. A common early sign is holding small print farther away to read it.

Which American Founding Father is generally credited with inventing bifocals, glasses split for near and far sight?

Benjamin Franklin, by one account, cut his lenses in half so that he could watch French speakers' lips at court. The word bifocals itself dates from 1824.