Shaking a fluid surface often results in standing waves known as Faraday waves, but with a non-Newtonian fluid like oobleck, at some frequencies it’s possible to incite other behaviors. Oobleck is shear-thickening, meaning that its viscosity increases when force is applied. This is what allows it to develop finger-like protrusions under high frequency vibrations.
This gives me the heebiejeebies. I don’t know how to spell that…
its a wonderful phenomena to observe :)