ANIMAL TRAP
A snap trap that sets itself when stood on end.
The operator stands the trap vertically and swings the spring-loaded jaw over through 180 degrees. The crossbar of the jaw cams a pivoted locking bar outward until the bar's trigger-engaging portion drops into frictional engagement with a trigger on the bait pedal, setting the trap without the operator touching the trigger. The mouse nibbles the bait; the unsupported weight of the bait pedal and bait acts to disengage the trigger, and slight downward pressure releases the locking bar. The jaw snaps back to the released position, striking the animal.
“It will be noted that one reason for the extreme sensitiveness of the trap is that the animal nibbling at the bait does not have to overcome the action of a spring or counterbalance weight, and as a matter of fact, the weight of the forwardly extending portion of the bait pedal and of the bait itself acts in a direction to disengage the trigger, so that a slight pressure on the bait or bait pedal is sufficient to release the jaw.”— John U. Lehn and Herman Drach, from the specification
And the world did not beat a path to their door.