MOUSE-TRAP
A snap trap made of four pieces, not counting the staples.
A wire frame pivots on staples driven into a wooden base and is held open by a wire spring resting on dead center against a crank arm. The mouse pulls at bait impaled on an arrow-shaped tongue punched from a flat metal trigger. The trigger's inner end lifts and knocks the crank arm off dead center. The spring expands and throws the wire frame down onto the animal.
“It will be noted that the frame which clamps the animal caught is composed of a single piece of wire, that another piece of wire forms the spring and the trigger is made from a piece of flat metal so that my entire trap is composed of but four pieces including the base and not counting the staples and the nail or pin 11.”— Roy Innes, from the specification
And the world did not beat a path to his door.