To perform this trick you need a pack of ketchup from a fast food restaurant. The packet needs to barely float in water. If it has too much air, it won't work. Put the packet into a plastic bottle filled with water and screw on the cap. If you squeeze the bottle, the packet will sink. Release the bottle and it floats. Barely press the bottle and it will stay in the middle. It is most effective if you use hand motions as the packets moves up and down in the bottle.
-- RickMach - 18 Mar 2007