A captive bolt gun is a tool used to incapacitate an animal prior to slaughter. It is typically pneumatic, but there spring-loaded and blank firing types as well. The operation of a bolt gun consists of placing the tip of the bolt on the forehead of the animal, equidistant from the eyes, and then activating the bolt release by pulling a trigger mechanism. This launches the bolt forward, either making a shallow wound and knocking the animal unconscious, or penetrating the skull and killing the animal instantaneously through brain trauma.
In either case, it allows the animal a quick, near painless death.