in the penetrating type, the stunner uses a pointed bolt which is propelled by pressurized air, spring mechanism, or a blank cartridge. the bolt penetrates the skull of the animal, enters the cranium, and catastrophically damages the cerebrum and part of the cerebellum. concussion causes destruction of vital centers of the brain, and an increase in intracranial pressure, the animal loses consciousness. this method is currently the most effective type of stunning, since it physically destroys brain matter (increasing the probability of a successful stun), while also leaving the brain stem intact and thus ensuring the heart continues to pump during the exsanguination. one disadvantage of this method is that brain matter is allowed to enter the blood stream, possibly contaminating other tissue with bovine spongiform encephalopathy (bse, colloquially known as mad cow disease).