A captive bolt pistol (also variously known as a cattle gun, stunbolt gun, bolt gun, or stunner) is a evice used for stunning animals prior to slaughter. Proper stunning is essential to prevent the pain and suffering of the animal through the bleeding (exsanguination) process (which is itself necessary to prevent meat spoilage) during the butchering process. The principle behind captive bolt stunning is a forceful strike on the forehead using a bolt to induce unconsciousness. The bolt may or may not destroy part of the brain, depending on which method is used. The bolt is a heavy rod made of non-rusting alloys, such as stainless steel. It is held in position inside the barrel of the stunner by means of rubber washers. The bolt is usually not visible in a stunner in good condition. The bolt is actuated by a trigger pull and is propelled forward by compressed air or by the discharge of a blank round ignited by a firing pin. After striking a shallow but forceful blow on (or through) the forehead of the animal, spring tension causes the bolt to recoil back into the barrel.