If you've never heard of a non-newtonian fluid, it is one that has a variable viscosity dependent on the rate of shear. To clarify even further, under quick loads, the fluid acts like a solid, and under slow loads, it acts like a liquid.

These properties make for some pretty interesting entertainment with the fluid when you put it on a reverberating speaker, or even try to run across a giant vat of it. See all the interesting properties of a non-newtonian fluid in brilliant slow motion above.