Porcupinefish, also called spiny puffer, is any of several fish with sharp, protective spines covering the body. These spines resemble porcupine quills. When an enemy or intruder scares a porcupinefish, the fish may enter a hole or crack in a rock and fill its stomach with water. The water causes the fish to inflate like a balloon, making its spines stick out. In most porcupinefish, the spines lie flat against the body when the fish are calm.