When I worked at James Cunningham Sons & Co. in Rochester, NY, I worked for an inventor named Andy Vincent. One day, he told me about his experiences developing an electric rat trap. The story goes something like this:
Sibleys department store had a grocery section and stored their goods in the basement, where they were plagued by rats. Somehow, they got in touch with Andy, who spent some time at night in the basement observing the rat behavior. He found their main "road" and placed a trap on it. But the rats wouldn't enter the trap; it had one end closed, with the other end activated by a switch in the floor. So he changed the trap by adding another open end, activated by the same switch.
The theory was that the rats would be trapped and in their panic would go into an adjoining chamber where they would be electrocuted; the bottom of the chamber would open to drop the dead rat out. Well, the rats would go into the trap, the doors would close, and the rats would just sit there analyzing the situation, until the doors opened again, then walk out.
So back to the drawing board!
The next step was to install a pad that would give a tickle jolt of electricity to the rat in the first chamber, causing it to go into the adjoining chamber and meet it's fate. Success at last! And that's how an inventor claimed victory over a common pest.
The reason this all came to mind is that I have seen rats in our back yard twice recently. They are known locally as "roof rats", but are a black rat. They eat citrus fruit. So instead of trying to build one of Andy's ingenious devices, I bought some D-Con. It's up on a wall held down by a brick so it won't fall into reach by our two Corgis. So far, the first box has been cleaned out, and the second box is untouched. Hopefully, my rat problem has been solved.