At school today the Physics teacher told the class (who didn't want to work, it being the last day of term) that if they all worked well, at the end of the lesson they could blow something up.
Having worked well they were presented with a box, supposedly containing all the necessary chemicals, within which was a baloon with 'April Fool' writen on it!
although I did trip over a chair in the hairdressers and give everyone else a good laugh, they thought I was the entertainment! 