When the raisins are put in HCl, why do the dance...move up and down??

Answer 1

I have to admit, I've never heard of this one, but I have a guess:

The acid is reacting to something in the raisin, causing bubbles of gas to be formed. Since the gas is less dense than the acid solution, the raisin becomes temporarily buoyant and rises, until the bubble escapes (or if the bubble/s is/are small enough, they may even become dissolved in the solution as they reach the surface of the raisin) Since raisins still possess some moisture, if the acid solution is strong enough, it may even be reacting to the water in the raisin (in a chemistry lab, one of the cardinal rules is that you always add acid to water, not the other way around, because a small amount of water added to acid will get violently ripped apart, splashing acid everywhere... the same thing may be happening to your raisin, but on a miniature scale)