Adding little hydrogel balls to a hot surface has an interesting effect as seen in this video. Hydrogels (as the name suggests) contain a lot of water but rather than melt or burst, the little balls are seen to bounce up-and-down on the hot surface making a high-frequency squeaking noise.
My thought on this is that it is related to the Leidenfrost effect. At the hot surface, the membrane is quickly heated and perhaps some small amount of vapor escapes causing the balls to bounce. However, I don't think this would have enough force to have them bounce so high. Perhaps the elasticity of the hydrogel plays a part.
Does anyone have an alternative idea?