A porcupine quill is a sharp, stiff spine found on the back of porcupines, which are rodents belonging to the family Erethizontidae. These quills serve as a defense mechanism, deterring predators with their barbed tips that can become lodged in the skin of attackers. Porcupines can have up to 30,000 quills, which they can shed when threatened. The quills are made of keratin, the same protein that forms human hair and nails. When a porcupine feels threatened, it raises its quills to appear larger and more intimidating. Unlike some other animals, porcupines cannot shoot their quills; instead, they rely on their ability to detach them easily when touched.