Ah cats, I hate cats. In fact, at my fifth grade invention convention, I created a device to catch cats. As I remember, it was called the 'Krispy Kitty Kat Katcher'. It was a fence with narrow set and very rough rope. I had to turn it in before I added the four inch nails though. The next part of my plan was to hook it up to an electrical outlet with copper wire and make it into an electric fence.
My other idea was the Krispy Kitty Kat Krusher. It was a simple deadfall device, with catfood blocked by a tripwire. When the cat would break the tripwire, it would release the deadfall and, I as always marketed it:
"From cat to splat, just like that!"
My final idea was the Krispy Kitty Kat Kooker. It was designed around a similar idea as the Krispy Kitty Kat Katcher, but it would use a box with cat food, with a pressure plate that controlled a bottle of gasoline that would be shot through an atomizer and lit with an electrode.
I was a messed up kid- and I still entertain the idea today (though now I know better than to cook, crush or catch cats).
-Penguin