METHOD AND A DEVICE FOR TRAPPING RATS, MICE AND THE LIKE
Counts the rats' visits before dropping them into carbon dioxide.
A rat enters a tunnel compartment and passes a photoelectric detection unit, which increments a visit counter. When the count reaches a preset limit, an electronic control unit releases a latch, and a curved drop door rotates under the animal's weight. The rat falls into a lower chamber pre-filled to approximately seventy percent with carbon dioxide from a pressure bottle, where it is anesthetized and killed within seconds. The door returns to its starting position by its own weight, and the dead animals collect in a removable, bag-lined drawer.
“The animals will thus drop directly down into an atmosphere of poisonous gas, which contributes to quick killing, which in turn means that the animals will not have time to communicate negatively with their fellow creatures.”— Per Rønnau, from the specification
And the world did not beat a path to his door.