My Nan had a rat trap. It worked on the same principle as the weedy little mouse traps that you can get, but it was much bigger, more powerful, and evil. A spring-loaded bar is triggered by the rat's attempt to take the bait, and it comes down to break the rat's neck. As a young kid, it took most of my strength to pull the bar back against the spring to set it, and if I accidentally caught my thumb in it, it hurt like hell.
After my grandad died, my Nan took in a lodger. He was the only person who used the shed where Nan kept the rat trap. I get the impression that he was not much liked by my family, although I had nothing against him. So it was more out of childish malice than anything else, that I figured that if I set the trap, put it away on the shelf in the shed alongside some other innocuous items to conceal it, maybe it might get him.
I had forgotten all about it until one day my father came to me, and explained carefully that it was a really bad idea to leave set rat traps where people might find them. The thing is, he couldn't keep his lips from twitching up at the end, so I knew I had struck gold.
There was one for sale at the car boot today. Happy memories.