Human Body
Your eyes see red, green and blue only
Three cone types cover the whole spectrum; every other colour is your brain mixing their signals. Some women carry a fourth cone type and see extra shades.
More in Human Body
Bone is stronger than steel by weight
Gram for gram, human bone outperforms steel in compression — a hollow lattice design gives it strength without the weight.
Your stomach rebuilds its own lining every few days
Stomach acid is strong enough to dissolve metal, so the lining replaces its cells every 3–4 days to avoid digesting itself.
Your brain runs on about 20 watts
Some 86 billion neurons fire constantly, yet the whole brain uses roughly the power of a dim light bulb — while consuming a fifth of your energy.
Your stomach lining rebuilds every few days
Stomach acid is strong enough to dissolve metal, so the lining replaces its cells constantly to avoid digesting itself.
You have more bacterial cells than human ones
Roughly 38 trillion microbes live in and on you — about as many as your own cells, and they weigh around two kilograms.
Goosebumps are a leftover from fur
Tiny muscles pull each hair upright to trap warm air and look bigger to a threat. It worked when our ancestors were hairy; now it just makes bumps.