As a result, fully conscious birds are hung upside down by their feet on metal shackles, suffering pain and terror as they are carried on a conveyor belt to the knife. Where stunning is used, industry reports indicate a high failure rate. All three methods can 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.
Many small plants use head-only stunning because they lack restraint equipment.
This type of stunning is reversible, and animals regain consciousness when they are not bled immediately due to slow hoists or other handling problems. The most severe stunning problems occurred in calf slaughterhouses. 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. Large animals, such as cattle, are particularly prone to torn ligaments and broken bones during the process.