Heat a solution, let it cool, and you’d expect it to sit there quietly. Instead, one touch can turn liquid to solid in seconds, releasing warmth as it goes. This is supersaturated sodium acetate, and the physics behind it is stranger than the party trick suggests. Sodium acetate trihydrate (CH3COONa·3H2O) melts at roughly 58°C. Heat it past that point and the crystal lattice collapses into solution. The clever part comes during cooling: if the liquid is clean and undisturbed, it can drop well below its freezing point without solidifying. It becomes supersaturated, holding far more dissolved salt than equilibrium should allow. Why does it wait? Crystallization needs a starting point. To form a stable solid, molecules must assemble into a tiny ordered cluster called a nucleus. Below a critical size, surface energy makes these clusters unstable and they redissolve. The system is stuck in a metastable state, energetically primed but kinetically trapped. Introduce a seed crystal or even ...