Back in the day of high school high jinks there was the widely held idea that if you wanted to get someone to wet themselve while asleep you put one hand in a bucket of cold water, the other in a bucket of warm water.
While we always talked about it on school trips etc, does it actually work? and how? why does have your hands in water produce such a reaction!
In the distant days of my youth I have persuaded a slightly intoxicated colleague to get up and go to the toilet by putting his fingers in a glass of lukewarm water as he slept. I can only imagine it sets the brain thinking "Water - now"!
Back in the old country we tried making this work for ages (hand in a bowl of lukewarm water) but could never get it too, although often we poured the water over them anyway to similar effect.