I had seen this particular demo going about on YouTube for a while, but it wasn’t until we tried it for a holiday program that I wanted to investigate it further.
The idea is that the cornflour is a non-Newtonian fluid; that is, it does not behave like a classical fluid, ie, water. It instead changes its consistency depending on the forces acting on it. At times it can flow and ooze. Other times it can feel and act like a solid.
Pour the mixture into a sound speaker, and find the right percussive action, and you get all kinds of spectacular behaviour.