That's an interesting little invention. Evidently the flexible clicker breaks off a tiny particle of garnet or silica which is sufficient to initialize the crytallization of the supercooled liquid.Neat!
Used to use sodium thiosulphate for the same effect in class. Using a new test tube helped prep the solution. Tiny scratches left on the interior surface of old, scrubbed tubes often initiated crystallization as you tried to chill them in ice water.
For fun with munchkins (little people) try a glass of beer or ginger ale. Pour slowly. Take a stainless steel fork. Scratch their initials or a happy face on the walls of the interior of the glass, and you'll nucleate bubble formation on your design on the microsctratches.
Same effect causes bubbles to seem to appear at the same impurity on your beer glass wall. Donald Howard Glaser noticed that in his beer...developed the hydrogen bubble chamber....got the Nobel Prize for it.
......and to think they don't think scientists get anything done while having a few cold beers.!
Hydrogen held under pressure as a liquid, has the pressure reduced by an oscillating piston....particles stream through the liquid...nucleation occurs on the ionization trail...a strobe flashes...takes a picture...the piston repressurizes the chamber...the bubble trail disappears. They do it again. See Gargamelle.