Porcupines use quills that cover their backs and tails to protect themselves, and these quills are mixed in with their regular hair. When threatened, porcupines turn their backs and try to shove their tails full of quills into would-be attackers.
Quills are special hairs that are sharp, and they vary in length from half an inch to 4 inches. When porcupines feel safe, the quills lay flat, but when they are scared, the quills stand on end. Before using their quills, they may make verbal noises or emit an odor to scare the predator away, but the quills are their primary defense.