There was a thread here a while back about practical jokes and someone said they made a box out of duct metal that simply had a switch on the top of it . It was a spring loaded switch and when you flipped the switch it had a capacitor in there that was charged by a 9 volt battery. Does any one remember this thread. It had a picture that showed roughly how to make it. It was quite a while back. I can't seem to find it. Does anyone have plans for such a thing? My boys are at the practical joking age. Thought this would be a good one to get them with.