 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.Supporters of cage traps say that they are the most humane form of trapping, and in some countries are the only method of trapping allowed.