Goose bumps

Goose bumps, also called goose pimples in British English, are the bumps on a person's skin at the base of body hairs which may appear when someone is tickled, cold, or feeling strong emotions. Goose bumps happen because of a reflex called piloerection.  Tiny muscles in the skin, called arrector pili, become tight and pull hairs upright. Many mammals have this reflex, for example, porcupines, which raise their quills when in danger, or sea otters when they spot sharks or other predators.

 References 

Category:Reflexes