There's a liquid you can run across, but you'll sink if you stand still

Ordinary liquids, like water or oil, have a viscosity that doesn't depend on how fast you move through them. Non-Newtonian fluids break that rule — their resistance changes dramatically depending on how quickly force is applied.

The classic homemade example is a mixture of cornstarch and water, sometimes called "oobleck": punched with a fist, or hit by the pressure of a fast-running foot, it behaves almost like a solid and pushes back hard, but slowly sink a hand into it and it flows like an ordinary thick liquid.

Thanks to this property, physics enthusiasts have managed to run across pools filled with the stuff — as long as they never stop moving. Stand still for even a moment and the liquid "softens" beneath you, and you slowly start to sink.

The mechanism: under a sudden shock, the starch particles jam together, blocking the free flow of water between them, while under slow movement they have time to slide apart and let the liquid flow freely.