Why do we get goosebumps?

You get goosebumps because tiny muscles at the base of each hair, called arrector pili, suddenly contract and pull the hairs upright, raising a little bump of skin around each one. The command comes from the sympathetic nervous system, the same system behind many fight-or-flight reactions, which is why cold and fear both set it off.

For a furry animal, this makes perfect sense. Standing hairs trap a layer of air that works like insulation on a cold day. And when an animal is angry or scared, bristling fur makes it look bigger and scarier: think of a frightened cat, or a porcupine raising its quills. Humans have lost most of that fur, so many consider our goosebumps a vestigial reflex, a leftover from hairier ancestors. The coat is gone, but the button to fluff it up is still wired in.

The odd part is how often emotions press that button. A horror film, nails on a chalkboard, or reliving the joy of winning a sports match can all do it. And the name? It comes from plucked goose skin, which is covered in bumps where the feathers were. French speakers look at a different bird: they get "chair de poule", hen's flesh.