Non-Newtonian fluid is a suspension of starch (e.g. cornflour) in water, sometimes called oobleck. The sudden application of force — for example by stabbing the surface with a finger, or rapidly inverting the container holding it — leads to the fluid behaving like a solid rather than a liquid. This is the "shear thickening" property of this non-Newtonian fluid. More gentle treatment, such as slowly inserting a spoon, will leave it in its liquid state. Trying to jerk the spoon back out again, however, will trigger the return of the temporary solid state. A person moving quickly and applying sufficient force with their feet can literally walk across such a liquid. (source en.wikipedia.org/wiki/Non-Newtonian_fluid)
