This is yet another reason to pay attention in class. I can see this being rather useful this halloween.
“This works because the substance is not “ice” as in water, but a different substance called sodium acetate trihydrate. Normally solid sodium acetate was melted into a liquid that was then supercooled to below its melting point. In this state, adding nucleation sites, like the crystals on my hand, rapidly causes the rest of the sodium acetate to crystallize.”