Drop some raisins into a pint of beer and watch them float up and down. I've done this with blueberries in blueberry flavored beer, Coconut pieces in Coconut flavored beer and I've heard of people doing it with Chunks of Jello. It works because carbon dioxide bubbles cling to the surface of the raisin or other small object. Once enough bubbles to lift the raisin accumulate it rises to the top. When it gets to the top the bubbles are released and gravity pulls the raisin back down. Have fun and let me know if you come up with any other ways to use this idea.