This thing is Hi Tech (tm). There is a big plastic-encased liquid bubble thingie, with SQUEEZE HERE TO ACTIVATE emblazoned on it. So you do, and you hear this popping sound as you break the plastic seal. Then, per instructions, you shake the whole doohicky vigorously, to mix the solid parts and the liquid parts, and it all gets cold.
Tres cool. Of course, it's probably toxic as all hell. Oh, yes, let's see. Contents: Ammonium Nitrate and Water. I think I shall be careful not to puncture the little plastic pouch, eh?
But it's still cool. (No pun intended.) (No. Really.) (Chill.) (har)