Water, water everywhere...

by Bob Bob
(UK)

A variation on the "disposable cups of water filling the room" classic. Instead of stapling all of the cups together, try the following: take two cups and tape each end of a piece of string to each cup. Repeat this for as many of the cups as you feel like (with the string hidden under all of the cups). This means that when one cup is picked up, it pulls another one over somewhere else. Your victim will think escaping the trap to be easy, and then after one or two attempts to clear up the cups they'll realise the catch!