Why do we get goosebumps?

Goosebumps happen when tiny muscles attached to your hairs tighten. Cold, fear, or a big feeling can make your nervous system send that order. Each hair lifts a bit, the skin puckers around it, and a patch of smooth skin becomes bumpy.

The charming oddity is that this made more sense when our ancestors were much hairier. Raised fur can hold warmer air close or make an animal look larger. On us, the old body trick remains, but the fur coat is mostly gone.