Some of the 'tricks' played on people mentioned here are not my (nor others by the sound of it) idea of fun. I had much milder things in mind when I originally started this topic. Not things like trying to scare people whilst they are negotiating slippery climbs, nor making them think they are about to drown.
No, I was thinking of light hearted little things to make you remember things with a smile.
For example, someone (never did find out who) put a fake skull in the bottom of our dig just after it started flooding on a regular basis. Most of us picked it up at one time or another thinking 'what's this floating rock?' It made us all jump a little bit, but it was obvious it was a fake one. Anyone who had a dodgy heart would never have made the long climb up the ladder to get back out anyway, skull or no skull!
Little yellow plastic ducks also appeared one week swimming around at the bottom.