Hot ice, everyone. Or supersaturation. I’ve done this in a lab and it is fun as hell. I’m going to explain the process of what the thing I did was, and assume it applies to what is going on in this gif. If I am wrong someone let me know.
I’m going to guess this is sodium acetate, as that’s what I worked with. You can make it with baking soda and vinegar. You very slowly add bits of baking soda to the vinegar and stir between additions - slow enough that you don’t get the volcano effect that kids love to make. Once the baking soda has been added, you boil it to further concentrate it, and stop boiling once a film has started to form over the surface. Covering the liquid to prevent evaporation and cooling it results in a supercooled liquid - a liquid that is actually at a temperature below its melting point. Something as simple as touching it - either with a fingertip or with another crystal, which could be what the ‘ice cube’ in the gif is - should activate the exothermic reaction that results in instant crystallization. And the crystals will be warm to the touch. Hence the name ‘hot ice’.
I did this in Chemisrty but we failed because our NaC2H3O2 got contaminated