Porcupines bristle up when alarmed, and a small muscle attached to each quill pulls it upright in the fur. When a porcupine chooses to fight its adversary rather than flee, it quickly jumps at its opponent, often skewering it with those bristled-out quills. This jumping movement is extremely fast and has given rise to the myth that a porcupine launches the barbs from a distance. The porcupine has an estimated 30,000 quills on its body and is thus not incapacitated even by the loss of several hundred quills during a fight. He's still armed and dangerous.
New quills grow in to replace lost ones.
There are no quills on this critter's muzzle, legs, or underside. On the face, the quills are only about a half-inch long, but on the back they may be up to five inches in length.