My family were playing games etc. at Christmas and one of them was where someone sits down and four people try to lift him by using one finger, under each knee and each arm. It couldn't be done. But then they all put their hands on top of his head, press down and quickly try to lift again and the person goes up high in the air! I'm sure some of you will have seen it and what I want to know is - is it a trick, or if not, how does it work?