This small, spiky animal can curl into a tight ball with spines sticking out in all directions. When they roll up, a special highly developed circular muscle that runs along the side of the body and across the rump and neck contracts and forms a “bag” into which the body, head, and legs are folded. They curl up if disturbed or frightened — only the strongest predators, such as the badger, can pry them open. They also sleep in this position, so are rarely caught unprotected.