Your body

A defence aimed at nothing

Why Does Pollen Make Some People Sneeze?

An allergy is your immune system mounting a real defence against something harmless, and the symptoms are the defence, not the pollen.

Let’s go →

They only kill one kind of thing

Why Don't Antibiotics Work on a Cold?

Antibiotics attack structures only bacteria have, so they do nothing to viruses — and every unnecessary course breeds resistance.

Let’s go →

Dead armour over a living pipe

What Is Bark For?

The rough outside is dead armour. The thin living layer just beneath carries the tree's food downwards, which is why cutting a ring round a trunk kills it.

Let’s go →

A windscreen wiper you never think about

Why Do You Blink?

Fifteen blinks a minute costs you half an hour of daylight a day, and screens halve that rate, which is exactly why they leave eyes feeling gritty.

Let’s go →

Four things in a river

What Is Blood Made Of?

Blood is mostly salty water carrying three cargoes: red cells that ferry oxygen, white cells that stand guard, and fragments that plug the leaks.

Let’s go →

The one blush you cannot fake

Why Do You Go Red When You Are Embarrassed?

Adrenaline opens the unusually wide blood vessels in your face — an honest signal precisely because you cannot start, stop or fake it.

Let’s go →

And a short list of exceptions

You Are Not Made of What You Were Made Of

Tissues replace themselves at wildly different speeds — days for gut lining, a decade for skeleton — and a few things are made once and never renewed.

Let’s go →

Stiff and springy together

What Are Bones Made Of?

Bone is a hard mineral laced with a stretchy protein, so it is strong without being brittle. It is also hollow, alive, and rebuilt thicker where loaded.

Let’s go →

Predicting, not just reacting

What Does Your Brain Do?

Your brain runs a constant prediction of what is happening and uses the senses to correct it. That is exactly why an illusion can fool you so completely.

Let’s go →

Fetching oxygen, dumping waste

Why Do We Breathe?

Breathing collects the oxygen that releases energy from food and dumps the carbon dioxide left over. The urge to breathe comes from the waste, not the air.

Let’s go →

Watching blood being cleared up

Why Does a Bruise Change Colour?

A bruise is blood spilled under unbroken skin, and its parade of colours is that blood being taken apart one stage at a time.

Let’s go →

Air that took a wrong turn

Where Does a Burp Come From?

Almost every burp is air you swallowed without noticing. Gas floats to the top of your stomach, and the way in is the only way out.

Let’s go →

The leaves are the spines

Why Does a Cactus Have Spines Instead of Leaves?

A cactus did not lose its leaves — it shrank them into spines to stop water escaping, and handed the job of feeding it to its green stem.

Let’s go →

A sudden gale, from inside

Why Do You Cough?

A cough is a pressure explosion: seal the airway, squeeze hard, then let go all at once, fast enough to scrape the whole tube clear.

Let’s go →

Something living in you, or something going wrong

Why Do You Get Ill?

Some illnesses are living things multiplying inside you and some are the body's own workings going wrong, and they need opposite treatments.

Let’s go →

Fluid that keeps going

Why Does Spinning Make You Dizzy?

Three loops of liquid in each ear sense turning, and when you stop the liquid does not, so your ears insist on a spin your eyes deny.

Let’s go →

A brain rehearsing offline

Why Do We Dream?

In one stage of sleep the brain replays and files the day while the body is locked still and the fact-checking parts are turned right down.

Let’s go →

Demand outrunning supply

Why Does Exercise Make You Puff?

Working muscles burn oxygen far faster than resting ones, so breathing and heart rate climb to keep up. Puffing is the delivery system catching up.

Let’s go →

A backstop for your fingertip

What Are Fingernails For?

Fingernails are a hard backstop that lets your soft fingertip press against something, making fine touch and picking things up possible.

Let’s go →

Living things too small to see

What Are Germs?

Thousands of bacteria fit across a full stop, and one doubling every twenty minutes becomes millions in a day. Feeling ill is largely your own response.

Let’s go →

Moving the focus point

How Do Glasses Help You See?

Sharp vision means light landing exactly on the retina, and a millimetre of extra eyeball is enough to blur it. A lens moves the focus back again.

Let’s go →

A reflex for fur you lost

Why Do You Get Goosebumps?

A tiny muscle tilts each hair upright. On a furry animal that is real insulation; on us it is a leftover reflex with nothing much left to lift.

Let’s go →

Cartilage turning into bone

How Do You Grow Taller?

Bones lengthen at soft cartilage zones near their ends, mostly during deep sleep, and when those zones harden for good your height is settled for life.

Let’s go →

A name that is probably wrong

Do Growing Pains Really Come From Growing?

Bones grow a few micrometres a day, which nobody could possibly feel — so growing pains are real aches with a badly misleading name.

Let’s go →

Dead rope, pushed out of a living hole

Why Does Cutting Hair Not Hurt?

A round follicle pushes out a straight strand and an oval one a curly strand, and grey arrives when the pigment cells at the root simply stop.

Let’s go →

Roughly one bacterium per human cell

About Half of You Is Not You

Your body is roughly half bacteria by cell count, mostly living in your gut, and the famous ten-to-one version of that figure turned out to be wrong.

Let’s go →

Vibration turned into signals

How Do You Hear?

Sound shakes your eardrum, three tiny bones amplify the motion, and a coiled tube sorts it by pitch before hair cells turn it all into nerve signals.

Let’s go →

A pump squeezing

What Is a Heartbeat?

A heartbeat is a muscle squeezing blood around a one-way loop, about once a second for a whole lifetime. The sound is its valves snapping shut.

Let’s go →

Two wards, two death rates

How We Found Out Germs Exist

One ward killed five times as many mothers as the other, and handwashing fixed it twenty years before anyone could name what was washed off.

Let’s go →

Harvey, 1628

How We Found Out Blood Goes Round

William Harvey proved blood circulates by multiplying: the heart pumps far more blood in an hour than the body could possibly make.

Let’s go →

An empty tube, squeezing anyway

Why Does Your Stomach Rumble?

Your stomach does not stop working when it is empty. It sweeps itself out, loudly, and hunger itself is a hormone that peaks on a schedule.

Let’s go →

Guess everything, keep what works

How Does Your Body Fight a New Germ?

Most of those shapes will never match anything at all. The ones that do are kept afterwards, so meeting the same germ in twenty years takes hours.

Let’s go →

A recipe, copied twice

Why Do You Look Like Your Parents?

One version can mask the other completely, so a trait can sit silent in a family for generations and then turn up in a child who never met it.

Let’s go →

Seven metres of grabbing

Why Are Your Intestines So Long?

Ridges multiply the area by three, villi by thirty and each cell's own fuzz by twenty again. The squeezing works upside down, so astronauts can eat.

Let’s go →

Drowning out one signal with another

Why Does Scratching Feel So Good?

Your liver can hurt but it cannot itch, because there are no itch fibres below the surface. And scratching releases chemicals that bring it back.

Let’s go →

Throw it all out, take back what you need

What Do Kidneys Actually Do?

Kidneys do not pick the rubbish out of your blood. They dump nearly everything small, then deliberately reclaim the water, salt and sugar.

Let’s go →

The chemistry room

What Is a Liver For?

Take two-thirds of a liver away and the rest grows back within a couple of months. No other large organ in you will do anything of the kind.

Let’s go →

Half a tennis court, folded up

Why Are Lungs Spongy Instead of Hollow?

A hollow bag would touch air only at its walls, so lungs split into millions of tiny sacs — around 70 square metres of surface, folded up.

Let’s go →

It does not, and that is the problem

How Does a Pill Know Where to Go?

A swallowed pill goes everywhere in your body and works only where its shape fits something, which is also exactly why side effects happen.

Let’s go →

No plumbing, no height

Why Is Moss Always Small?

Moss has no pipes to lift water, so every drop soaks from cell to cell — and soaking only works across millimetres, which sets its height.

Let’s go →

Only ever pulling

How Do Muscles Move You?

Muscles can only pull, never push, so they come in opposing pairs and use bones as levers to turn a short pull into a much larger movement.

Let’s go →

An alarm, not a measurement

Why Does It Hurt?

Pain is not damage arriving at your brain but your brain deciding an alarm is worth sounding — which is why a paper cut can scream at you.

Let’s go →

It is holding your neck, not your head

Why Does a Pillow Help You Sleep?

Lying down leaves a gap between your head and the mattress. A pillow fills it, so no neck muscle has to hold your head up for seven hours.

Let’s go →

A net, cast in seconds

How Does a Cut Stop Bleeding?

The scab is only a lid. Underneath it new skin creeps in from both edges, and when it meets in the middle the crust has nothing left to hold on to.

Let’s go →

Green, but not a plant

Is Seaweed a Plant?

Land plants all descend from one green ancestor. Seaweeds come from three separate lines, and many lift their fronds to the light on gas bladders.

Let’s go →

Muscles working for the heat, not the movement

Why Do You Shiver When You Are Cold?

Shivering makes your muscles do deliberately useless work, because a muscle is a poor engine and most of its effort comes out as heat anyway.

Let’s go →

Light in, picture built

How Do Your Eyes See?

Eyes turn light into nerve signals. The picture you see is assembled afterwards by the brain — patched, corrected, and rather less direct than it feels.

Let’s go →

More than a wrapper

What Does Your Skin Do?

Skin is four things at once: a barrier that keeps the world out, a thermostat, a sense organ, and a surface that entirely replaces itself as it wears away.

Let’s go →

Maintenance time

Why Do We Sleep?

Sleep is when the body repairs itself, the brain files what happened, and the whole thing gets flushed clean. Far too valuable to be optional.

Let’s go →

Catching actual molecules

How Does Smelling Work?

Around 400 receptor types, each waiting for a particular molecular shape, combine into trillions of smells — and into most of what you call taste.

Let’s go →

Blasting the nose clear

Why Do We Sneeze?

A sneeze is a reflex, not a decision: irritated nerves in your nose trigger a blast of air fast enough to clear them — and to spread germs remarkably well.

Let’s go →

Taken apart, then absorbed

What Happens to Food You Eat?

Nothing is absorbed until it is molecule-sized. Acid unravels proteins, but the real work happens in seven metres of small intestine folded very small.

Let’s go →

Cooling by evaporation

Why Do We Sweat?

Sweat cools you only as it evaporates, because evaporation carries heat off your skin. Hence a breeze helps, and humid heat is so much harder to bear.

Let’s go →

Five basics, plus your nose

How Does Taste Work?

Your tongue detects only about five things. Everything else you call flavour is smell, arriving at your nose from the back of your own mouth.

Let’s go →

Three kinds of tear

Why Do We Cry?

Your eyes make three different tears: a constant film for maintenance, a flood to rinse irritants out, and a chemically different one for feelings.

Let’s go →

A toolkit in your mouth

Why Do Teeth Have Different Shapes?

Chewing works by multiplying surface area, and three tooth shapes split the job: chisels at the front, cones for gripping, millstones at the back.

Let’s go →

A saltiness detector

How Does Your Body Know You Need a Drink?

Thirst is not a dry mouth. A small patch of brain is measuring how salty your blood has become, and it switches off the moment water is on its way down.

Let’s go →

Several senses at once

How Does Touch Work?

Touch is not one sense but several — pressure, temperature, pain and stretch — and most of it reports change rather than steady contact.

Let’s go →

A rehearsal

How Do Vaccines Work?

A vaccine shows the immune system a harmless preview of a germ, so the real thing arrives to find a defence already rehearsed and waiting for it.

Let’s go →

Two flaps, flapping very fast

How Do You Make Your Voice?

Whisper and the folds never touch — it is only rushing air, shaped the same way, which is why a whisper is still perfectly understandable.

Let’s go →

A bag that reports on itself

Why Can't You Just Hold It Forever?

Two tubes trickle into it continuously, the first polite signal arrives at about a third full, and cold weather really does make you produce more.

Let’s go →

Never far from water

What Is an Amphibian?

Frogs, toads, newts and salamanders share bare damp skin they breathe through and jelly eggs with no shell, which keeps them all near water.

Let’s go →

Smelling with your forehead

What Are an Insect's Antennae For?

An insect's antennae are not feelers but mostly its nose: pitted surfaces catching single scent particles, two of them giving direction.

Let’s go →

The fastest-growing bone there is

Why Do Deer Grow New Antlers Every Year?

Antlers are bone grown and discarded every year, which lets a deer show its condition honestly and cheaply repair a broken one.

Let’s go →

Ready to run, or helpless and blind

Why Are Baby Animals Born So Different?

Some babies are born nearly finished and some barely started, and which one depends on whether the mother has a safe place to leave them.

Let’s go →

Shouting at the world and listening back

How Does a Bat See in the Dark?

A bat crosses a pitch-black cave by shouting too high for you to hear and timing the echoes — and its wings are hands with enormous fingers.

Let’s go →

Turning round in mid-air

Why Does a Cat Always Land on Its Feet?

A falling cat has nothing to push against, and turns over anyway: it tucks one end in and leaves the other out, then swaps, twisting each half in turn.

Let’s go →

Teeth in the wrong place

Why Do Chickens Swallow Stones?

A chicken has no teeth at all. It swallows small stones on purpose and grinds its food against them in a muscular gizzard further down.

Let’s go →

A stomach with four rooms

Why Does a Cow Chew All Day?

Grass is nearly indigestible, so a cow ferments it with microbes in a huge first stomach, brings it back up, and chews the same mouthful twice.

Let’s go →

An hour underwater, without trying

How Does a Crocodile Hold Its Breath So Long?

A crocodile lies on a riverbed for an hour by slowing its heart to a crawl and sending blood only where it matters — brain and heart.

Let’s go →

A nose that catches smells

Why Is a Dog's Nose Wet?

The bits of stuff that carry a smell stick to damp skin, so a wet nose holds on to what a dry one would let blow straight past.

Let’s go →

You are what you eat

Why Are Flamingos Pink?

The pink is not theirs. Pigment from the algae and shrimp they eat is carried into each feather as it grows, so the colour is eaten first.

Let’s go →

Catching what you cannot see

How Does a Fox Hunt Under Snow?

A fox catches a mouse it never sees by comparing what each ear hears, tilting until it has the depth, then diving head-first at the sound.

Let’s go →

Seven bones, same as yours

Why Is a Giraffe's Neck So Long?

A giraffe has the same seven neck bones you do, each one enormous, plus a very strong heart and valves that let it survive bending down.

Let’s go →

Standing on almost nothing

How Do Goats Climb Cliffs?

A goat stands on ledges narrower than its own hooves. Each hoof splits into two toes with a hard gripping rim around a soft rubbery pad.

Let’s go →

An argument without a fight

Why Does a Gorilla Beat Its Chest?

Chest-beating is an honest advertisement of size, carried far enough that a rival can decide to back down long before anybody has to get hurt.

Let’s go →

Two ways to rent a stomach

Why Do Grass-Eaters Have Such Different Insides?

No animal can digest grass, so every grass-eater rents microbes — and whether it keeps them before the stomach or after changes everything else about it.

Let’s go →

Everything else was left behind

Why Do Horses Run on One Toe?

A hoof is a single huge toenail, and losing the other toes made the leg light at the bottom, which is what makes a horse fast.

Let’s go →

A leg that locks

Why Do Horses Sleep Standing Up?

A hook of bone clicks a horse's knee into a catch, so standing costs no muscle and it can doze upright, lying down only for its deepest sleep.

Let’s go →

Sticky feet and a very fast eye

How Does a Fly Walk on the Ceiling?

A fly lands upside down on clawed, glue-footed pads, sees your hand coming far sooner than you expect, and tastes whatever it stands on.

Let’s go →

Running the engine hot

Why Does a Hummingbird Eat All Day?

Wings beating fifty times a second and a heart running past a thousand a minute add up to nearly its own weight in nectar taken in before dark.

Let’s go →

No brain, no heart, no bones

How Does a Jellyfish Live With No Brain?

A jellyfish has drifted the seas since before there were trees with no brain, heart, bones or blood — just a net of nerves and a bag of water.

Let’s go →

A meal nothing else wants

How Does a Koala Eat Poisonous Leaves?

Eucalyptus is toxic to almost everything, which is exactly the point: a koala took the job nobody was competing for, and its liver pays the bill.

Let’s go →

Borrowing warmth instead of making it

Why Do Lizards Sit in the Sun?

A lizard eats a small fraction of what a mammal its size needs, because it buys its warmth from the sun instead of paying for it with food.

Let’s go →

Milk, hair and a warm inside

What Makes an Animal a Mammal?

A whale, a bat and you are all in one group. Milk is the test that never fails, with hair and home-made body heat as the other two marks.

Let’s go →

Two lives, one animal

Why Do Some Animals Grow a Second Body?

Some animals grow a whole second body because the job of eating and the job of travelling and breeding need completely different machines.

Let’s go →

If the head fits, the mouse fits

How Does a Mouse Fit Through a Gap?

A mouse pushes through a hole the width of a pencil because nothing behind its skull is locked at a fixed width, not even the shoulders.

Let’s go →

A fifth hand

Why Can a Monkey Hang by Its Tail?

African and Asian monkeys never evolved one in thirty million years of similar forest — a reminder that evolution does not find every good answer.

Let’s go →

It is not the bite, it is you

Why Does a Mosquito Bite Itch?

A mosquito bite does not hurt going in. The insect spits to stop your blood clotting, and the itch is your own reaction to that spit.

Let’s go →

Growing out of your own container

Why Do Animals Shed Their Skin?

A snake crawls out of its skin in one piece because it cannot grow inside it — and the hours before the new one hardens are its most dangerous.

Let’s go →

And it stops one of them to swim

An Octopus Has Three Hearts and Blue Blood

An octopus runs on copper-based haemocyanin rather than iron-based haemoglobin: blue, good in cold water, and inefficient enough to need three hearts.

Let’s go →

A bear with a meat-eater's stomach

Why Do Pandas Only Eat Bamboo?

A panda has a meat-eater's short gut and eats only a tough grass, so it copes by chewing for half the day and spending almost no energy.

Let’s go →

No lips, no teeth, no vocal cords

How Does a Parrot Talk?

A bird's voice box sits at the fork of its windpipe, so each branch works separately and some birds hold two notes at once — a duet with themselves.

Let’s go →

A net, not a bag

What Is a Pelican's Pouch For?

Eleven litres is about three times what a pelican's stomach could hold, and the same thin skin flutters in the heat to cool the whole bird down.

Let’s go →

Choosing the tame ones

How Did Wild Animals Become Pets?

Nobody set out to invent the dog. People kept the calmest wild animals to breed, over and over, until calm was ordinary and the looks changed too.

Let’s go →

Seeing by touch

Why Do Raccoons Feel Everything With Their Hands?

A raccoon's front paws sense more detail than its eyes do, so it explores by touch — especially at night, and especially with wet hands.

Let’s go →

The group that left the water

What Makes an Animal a Reptile?

Scaly skin and an egg with a shell are what made reptiles the first backboned animals able to live a whole life away from water.

Let’s go →

Two animals, one shape

Is a Salamander a Lizard?

A salamander looks like a lizard and is not remotely related to one. The wet skin gives it away: it is an amphibian, and it breathes through that skin.

Let’s go →

Senses you do not have

How Does a Shark Find Its Food?

A shark swings its head to compare nostrils, and its teeth sit in gum rather than bone, so a fresh row rolls forward through thousands in a lifetime.

Let’s go →

A whole body doing the work of feet

How Does a Snake Move With No Legs?

A forked tongue samples two places at once, so a snake smells in stereo, and its jaw comes in two halves that walk over a meal wider than its head.

Let’s go →

One part, a dozen jobs

What Is a Tail For?

A tail can be a rudder, a balance pole, a fifth limb, a fly swat, a blanket or a shout across a field — whatever that animal needs most.

Let’s go →

Half a millimetre long

The Animal That Was Left Outside a Spacecraft and Lived

A tardigrade can dry itself into a barrel called a tun, stop being metabolically alive, and survive vacuum and radiation — then rehydrate and carry on.

Let’s go →

A shell that is part of the animal

Can a Tortoise Come Out of Its Shell?

Because the ribs grew outwards, a tortoise carries its shoulder blades inside its own ribcage — true of no other backboned animal on the planet.

Let’s go →

It depends on who does the delivering

Is Venom the Same as Poison?

Venom is injected by the animal, poison is only dangerous if you eat or touch the animal — and both are made of the same kinds of chemicals.

Let’s go →

Eating what would kill you

Why Don't Vultures Get Ill?

A vulture eats meat that has been dead for days and walks away well, because its stomach acid destroys the bacteria and their poisons.

Let’s go →

Measuring the dark

What Are Whiskers For?

A cat's whiskers are not for stroking. They are levers in nerve-packed follicles, measuring gaps and air movement in total darkness.

Let’s go →

Hitting a tree, all day

Why Doesn't a Woodpecker Get a Headache?

It hammers wood twenty times a second and walks away fine. Being small is most of the reason: a tiny brain packed tight has no room to slosh.

Let’s go →

A wire crossed

Why Does Ice Cream Give You a Headache?

Press your tongue flat against the roof of your mouth and it stops. The nerve rarely hears from the palate, so it blames the forehead instead.

Let’s go →

Kind to the blade, unkind to germs

Why Are Chopping Boards Made of Wood?

Wood is soft enough to spare a knife edge and wicks moisture away from bacteria. Keeping separate boards, though, matters far more than the material does.

Let’s go →

Your body is already predicting

Why Is It Hard to Sit Still to Music?

Muscles answer about a fifth of a second late, so clapping on the beat means deciding before it arrives. A crowd syncs without arranging anything.

Let’s go →

Ridges that grip and feel

Why Do We Have Fingerprints?

Fingertip ridges channel water away so wet things can still be gripped, and they turn fine texture into vibrations your touch sensors are able to read.

Let’s go →

A squashed cable

Why Does Your Foot Go to Sleep?

It is the nerve being squeezed, not the blood supply, and the thick fibres wake first, which is why it goes tingling, then aching, then normal.

Let’s go →

Faster sound, same vibration

Why Does Helium Make Your Voice Squeaky?

Sound travels far faster in helium, so the resonances of your unchanged throat leap upward. Your vocal cords carry on buzzing at exactly the same pitch.

Let’s go →

A muscle misfiring

What Causes Hiccups?

An irritated nerve jerks the diaphragm into an unplanned gulp, and about 35 milliseconds later the vocal cords snap shut on it. That snap is the sound.

Let’s go →

It steals heat faster

Why Does Metal Feel Colder Than Wood?

Metal and wood in the same room are the same temperature. Metal only feels colder because it pulls heat out of your hand very much faster.

Let’s go →

A chemical booby trap

Why Does Chopping Onions Make You Cry?

The gas is a bulb's defence against animals that dig, and we are collateral damage. A chilled onion and a sharp blade both release far less of it.

Let’s go →

Your brain saw it coming

Why Can't You Tickle Yourself?

A machine that copies your own hand movement half a second late really does tickle you, because the prediction your brain made no longer lines up.

Let’s go →

Cooling and catching

Why Do We Yawn?

Yawning seems to cool the brain rather than fetch oxygen, and it spreads between people along the circuits that carry empathy — strangers catch it least.

Let’s go →

A hidden middle

What Keeps Things From Falling Over?

Every object has a balance point. It stays upright only while that point sits over its base, which is why a wide base and low weight rarely tip.

Let’s go →

Light, sorted

Where Do Colours Come From?

White light is every colour at once. An object's colour is the one slice it refuses to absorb and throws back at your eyes — the leftovers, in other words.

Let’s go →

You would not get stronger

What If Gravity Were Half as Strong?

Your jump would double and nothing about you would improve: bones weaken, trees overreach, and the planet slowly leaks its air away.

Let’s go →

It makes nothing — it slows

Does a Coat Make You Warm?

A coat makes no heat of its own. It traps still air, which slows the escape of the warmth your body is already producing every second.

Let’s go →

Not the chair, not this page

You Have Never Touched Anything

Solid contact is a force, not a meeting — the outer electrons of two surfaces repel each other hard enough that nothing ever quite arrives.

Let’s go →

Newton's third law

Every Push Has a Push Back

You cannot push anything without it pushing back exactly as hard. That pair of forces is what makes walking, swimming and flying possible at all.

Let’s go →

Rubbed the wrong way

Why Do You Get Shocks?

Rubbing moves electrons by the billion, and they sit on you until the pile-up can rip air apart to escape. A door handle can hit 3,000 volts harmlessly.

Let’s go →

About a hundred watts of it

You Are Glowing Right Now

Warm objects radiate light whose colour depends on their temperature — yours is infrared, invisible to us and perfectly obvious to the right camera.

Let’s go →

A sugar you cannot digest, but bacteria can

Why Do Beans Make You Windy?

Beans carry a sugar humans have no enzyme for, so it reaches the large intestine intact and the bacteria living there ferment it, giving off gas.

Let’s go →

Most of it is smell

Why Does Coffee Smell Better Than It Tastes?

Coffee's appeal is almost entirely aroma, because the tongue only reports bitter and sour and the nose reports hundreds of things.

Let’s go →

A sensor told a lie

Why Does Mint Feel Cold?

Mint cools nothing at all. Menthol holds your cold sensor open, so the nerve reports cold while the thermometer never moves. Chilli does the same trick.

Let’s go →

A chemical that lies to your nerves

Why Are Some Peppers Hot?

A chilli is not actually hot. It carries a chemical that opens the nerve reporting high temperature, so the burn is a signal about nothing.

Let’s go →

A fruit that eats you back

Why Does a Pineapple Sting Your Mouth?

The enzyme that tingles is the one that tenderises steak and stops a jelly setting — and every diamond on the skin was once its own flower.

Let’s go →

A skin you cannot digest

Why Does Sweetcorn Come Out Whole?

Each kernel is wrapped in cellulose, which no human enzyme can cut, so the wrapper survives the journey while the inside is absorbed.

Let’s go →

Scrubbing, and rebuilding

What Is Toothpaste Actually Doing?

Most of the cleaning is the brush. The paste is mild grit, detergent and flavour, plus the fluoride that actually rebuilds the enamel.

Let’s go →

An argument about very large numbers

Every Breath You Take Has Been Breathed Before

A single breath holds more molecules than the atmosphere holds breaths — so an old one, well mixed, is almost certainly inside the breath you just took.

Let’s go →

When sweat stops working

Why Do Some Hot Days Feel Worse Than Others?

You cool down by evaporating sweat, and humid air is already close to its water limit. It will not take any more, so your main cooling system simply stops.

Let’s go →

Losing your warm coat of air

Why Does Wind Make You Colder?

Your body heats a thin layer of air around your skin, and wind keeps stealing it. That is why you lose heat far faster than the thermometer suggests.

Let’s go →

Buying time, by millimetres

How Does a Helmet Protect a Head?

A helmet does not make your head harder. It crushes, which stretches a sudden stop over more time and cuts the force a brain must survive.

Let’s go →

One foot always down

Why Is a Scooter Easier Than a Bike?

A scooter is easier than a bicycle because you stand low with a foot free, so a wobble is corrected instead of becoming a fall.

Let’s go →

It notices charge, not pressure

How Does Glass Feel Your Finger?

A touchscreen never notices pressure. It measures charge draining into the salty water you are made of, at every crossing of a wire grid.

Let’s go →

Not what you think

Why Do Astronauts Float?

Gravity 400 km up is still 90 per cent as strong as at your feet. Astronauts float because the station falls around Earth and never lands — and so do they.

Let’s go →

Working outside

What Is a Spacewalk Like?

Space offers nothing — no air, no warmth, no up. A spacewalk means wearing a personal spacecraft, tethered to the one you just climbed out of.

Let’s go →