Non-Newtonian fluid

A non-Newtonian fluid is a substance that changes viscosity under stress or shear forces, suddenly acting more like like a solid than a liquid. Silly putty, a toy from the 1960's, is a silicon plastic that acts like a soft putty. But make a ball, throw it forcefully at the floor, and it will shatter like hard plastic - into pieces of soft, pliable putty.

Mixing cornstarch and water in the right proportions will make a fluid the consistency of dairy cream that you can literally walk across, so long as you slap your feet down hard enough.

Corn starch and water. Really.
About four.

So you don't have to watch the whole thing:
It's really a liquid.

I'm fascinated by the counter-intuitive aspects of the real world, from examples from cognitive psychology to the weirdness of quantum electrodynamics. I think that cherishing these things helps keep up one's sense of skepticism and critical thinking.