ANIMAL-TRAP.
A wire loop the animal must attempt to walk through.
Two spring-tensioned wire arms extend from a coil, one bent into an open loop set across the mouth of a den. The other arm is held retracted by a sliding detent, whose trigger arm extends across the loop opening. The animal, passing through the loop, disturbs the trigger arm; the detent releases and the spring arm sweeps across the loop, pinning the animal against the side member. A spring tongue engages notches on the loop to prevent the animal from forcing the arm back.
“The trap may be set across the den of the animal to be caught so that the animal must pass through the loop in entering or leaving the den, and it can also be set across muskrat dens beneath the water. The trap can also be used in various other ways and it is highly efficient in operation.”— Thomas J. Ellison, from the specification
And the world did not beat a path to his door.