We had one of our peers admitted for observation after he hit his head whilst playing rugby, he was one of my friends. anyway he ws only in for a short time, he started to become cheeky and sarcastic so I thought I will get you mate. When he asked for a bottle we put a little mecuricrom and a small amount of effurence (sorry my spelling is shocking) and gave him the bottle, as he passed urine this in turn 5reacted with the substance we had added and frothed all over the place, he really freaked hehe serves him bloody well right for the cheek;)