In a tall glass or jar, fill it with water about half way and add the vinegar and baking soda to the water. It will begin to fizz.
Drop raisins into the mixture one at a time. They will sink at first, then they will rise to the surface, then sink again.
They should continue to do this for about an hour.
Why does this work? Because combining vinegar and baking soda creates bubbles of carbon dioxide. The bubbles collect on the raisins and "lift them up". At the surface the bubbles are released, then the raisins sink and the process begins again. Cool huh?!