A humane trap is a cage with a door on one end which can be lifted up and set in place with a small hook. The door is connected to a flat metal trip plate on the bottom of the trap. The trap is baited by placing food at the back of the trap, past the trip plate.
When an animal enters the trap, the weight of its paw on the trip plate triggers the door to shut behind it. The trip plate is far enough away from the door so that the animal is not harmed.