Oobleck gets its name from the Dr. Seuss book called Bartholomew and the Oobleck, because, well, oobleck is funny and strange. Oobleck is a special type of slime with properties of both liquids and solids. If you squeeze it, it feels solid, yet if you relax your grip, it flows through your fingers. If you run across a pool of it, it supports your weight, but if you stop in the middle, you'll sink like its quicksand. Do you know how oobleck works?
Oobleck is an example of a non-Newtonian fluid. A Newtonian fluid is one which maintains constant viscosity at any given temperature. Viscosity, in turn, is the property that allows liquids to flow. A non-Newtonian fluid does not have a constant viscosity. In the case of oobleck, viscosity increases when you agitate the slime or apply pressure.
Oobleck is a suspension of starch in water. The starch grains remain intact rather than dissolving, which is the key to the slime's interesting properties. When a sudden force is applied to oobleck, the starch grains rub against each other and lock into position. The phenomenon is called shear thickening and it basically means particles in a dense suspension resist further compression in the direction of shear.
When oobleck is at rest, the high surface tension of water causes water droplets to surround the starch granules. Water acts as a liquid cushion or lubricant, allowing the grains to flow freely. Sudden force pushes the water out of the suspension and jams the starch grains against each other.