Cage traps are designed to catch live animals in a cage. They are usually baited, sometimes with food bait and sometimes with a live "lure" animal. Common baits include cat food and fish. Cage traps usually have a trigger located in the back of the cage that causes a door to shut; some traps with two doors have a trigger in the middle of the cage that causes both doors to shut. In either type of cage, the closure of the doors and the falling of a lock mechanism prevents the animal from escaping by locking the door(s) shut.