TRAPPING METHOD AND APPARATUS
Cannot be sprung unless two pressure plates are depressed at the same time.
The animal enters an elongated cage through an open end whose door is held raised by two independent release hooks. Each hook connects by a linkage rod to its own pressure plate, one near the entrance and one farther inside; pressing either plate alone does nothing. When the animal is long enough to depress both plates simultaneously, both hooks pivot rearward and the door swings shut under gravity. A torsion spring then forces a bracing plate against the closed door so the occupant cannot push it back open.
“The design of the trap precludes the possibility of inadvertently trapping smaller animals that do not meet the size requirements of the trap's capture mechanism.”— John Humphrey, from the specification
And the world did not beat a path to his door.