[scott] had a need to capture a mouse and wanted to learn about how to program an arduino, so he built an Arduino controlled mousetrap. It is made from things he had laying around the house, like some Tupperware containers and wooden rods. The program is pretty simple, when a trip wire is touched, the servo jerks the wooden rod out of the way, closing the container. You can see it working after the break. The trip wire seems like a big failure point. he states that it is just a wire, slightly above a tin foil strip. That seems like it would only be a tiny area that the mouse would need to touch to trigger it. What better switch could he design as cheap and quick as possible?
