I don't know how I discovered I could do it, but my friends used to make me look our Maths teacher in the eye and utter some kind of curse under my breath. It never did him any harm, but ALWAYS gave him an attack of clumsiness, like he'd forget what he was saying or drop his chalk. I don't know if I can still do it, 'cos I've got too much of a conscience now, but whenever you have an attack of clumsiness, look someone in the eye and tell them it's their turn. Now that DOES work!!!