I know the one you're talking about. Just stand with one arm hanging at your side and pressed against a wall/edge of a doorframe/whatever, push your hand as hard as you can into the surface, while keeping your arm pointed down, for about 60 seconds, then move away fro the surface and relax your arm. Et Voila, the amazing floating arm! My boyf showed me another one recently, and I'm racking my braing trying to think of it. Will ask him later on, and post it for you