Where stunning is used, industry reports indicate a high failure rate. Currently the industry uses three methods to stun animals, all of which cause tremendous pain and suffering. If captive bolt guns are improperly placed or if the gun is poorly maintained, the animals are not stunned, and will be in severe pain from a partial impact. Cardiac arrest stunning kills the animals by stopping the heart, and animals can feel painful heart attack symptoms. Insufficient cardiac electrical stunning also results in paralyzed animals that feel everything.
Many small plants use head-only stunning because they lack restraint equipment.
This type of stunning is reversible, and animals can regain consciousness if they are not bled immediately due to slow hoists or other handling problems. The most severe stunning problems occurred in calf slaughterhouses. Under the federal Humane Slaughter Act, animals are supposed to be stunned prior to slaughter. In addition to excluding poultry from stunning requirements, the law excludes ritual slaughter, such as kosher and halal. At hundreds of ritual slaughterhouses, a chain is wrapped around one of the animal's rear legs and the frightened, conscious animal is hoisted into the air, kicking and thrashing.