...actually, it's a pellet of “dry ice” floating on a shallow bed of dark blue water and shooting off geysers of carbon dioxide as it warms up. The dry ice is solid CO2 which sublimates directly to gas as it warms up (skipping the liquid phase altogether).
It is mesmerizing to watch. Particles glide along the surface, spin, and merge when they touch. Here is a very cool video of the icy bodies spinning and shooting around.