The premise is light but the execution is a decent plate tutorial in disguise. The opening titles of the television series show sand-like patterns forming on a surface, and Mould's read is that they are two-dimensional standing waves. He builds a square plate rig and works through the modes to see how close he can get.
What makes it useful beyond the gimmick is the attention to why particular figures appear at particular frequencies, and how much of the on-screen result depends on drive amplitude and powder choice rather than frequency alone. That is the variable most first-time builders under-appreciate: the same frequency gives a different-looking figure at different volumes.
Thirteen minutes, well shot, and it pairs with his earlier couscous Chladni video, which covers the basic phenomenon at a slower pace.