Building a Better Mouse Trap
Definitely not a pretty build, but at least it works!
Sometime in 2002 I had a mouse rooting around the house and set about building a live trap using LEGO. It didn't work very well. The mouse triggered it but managed to escape, and then left on its own before I had a chance to improve the design.
So when another mouse moved in sometime in 2006, I was pretty excited to go about building a better mousetrap. Not more than half an hour after setting it up, with nothing more than some old bread as bait, I heard the door snap shut and ran downstairs to find my first catch.
Of course it turned out there were two mice on the loose. I caught the other one a couple of nights later. Luckily neither one was trapped for very long, so they didn't have an opportunity to chew their way out. Both mice were released unharmed in a not so nearby wooded area.