Why won't these balls stop squeeking and jumping!? (i.e. the transition from elastic to equilibrium Leidenfrost with hydrogel spheres)

When hydrogel spheres are dropped onto hot surfaces, they harvest mechanical energy and squeek and bounce for several minutes. This commotion is related to the Leidenfrost effect, whereby a liquid drop above a hot surface floats on a cushion of vapor. Why can't hydrogels also do this "normal" floating Leidenfrost? In this talk, I will show that they can and explain how. Aside from shushing these squeeky hot bouncers, creating hovering hydrogels opens up the possibility to direct their dynamics by molding them into smart shapes.