Press a coin into the middle of your forehead until it sticks there. Then lean your head forward, and tap the back of your head until the coin falls into your hand. This is very easy to do with a little practice!
Now ask one of your friends if they would like to try it. Press the coin into their forehead, but in a sneaky move, remove the coin so they will think it''s still there.
No just watch and enjoy as they continue to tap the back of their heads - giving the rest of you a jolly good laugh!