What makes Goosebumps?
When a person gets cold, or angry or frightened, he may get little bumps on the skin called “gooseflesh,” or “Goosebumps,” caused by tiny muscles in the skin. Every hair has a muscle attached to its root. When a person gets cold (or frightened) these tiny muscles tighten up.
They produce little bumps on the skin and make the hair stand on end. Then the hair forms a thicker coat and keeps more air near the body for better protection against the cold.
Since man has lost most of his body hair, the added protection does not amount very much for him. In furred animals or birds, which show the same response, the insulting effect is considerable.
When an animal, such as cat, is startled, the same muscles make its fur stand on end just as they do when the animal is cold. It looks larger and more dangerous than it really is, and may frighten away its enemy.-Dick Rogers