Mixing cornstarch and water results in a non-Newtonian fluid called oobleck. The two components do not chemically react, although weak interaction forces between the cornstarch molecules and the water molecules do arise.
Fluids can be divided into Newtonian and non-Newtonian based on the way they react to applied force. Newtonian fluids, such as water, experience higher deformation as more force is applied to them. Non-Newtonian fluids, such as oobleck, experience less deformation the more force is applied. It was only fairly recently, in 2012, that a team of researchers was able to formulate a sound hypothesis as to what causes oobleck to behave the way it does. Scientists suspected that the oobleck hardened because it transferred applied mechanical force to the walls of the container. The hardening is now attributed to the cramming of spaced starch particles close to one another when force is applied.
Interesting shapes can be created by placing oobleck on a speaker or vibrating table, which cause the material to harden as the mechanical waves pass through it. Other examples of non-Newtonian fluids include ketchup, quicksand and silly putty. The non-Newtonian behavior of quicksand is what makes it so dangerous; the more a person struggles to escape quicksand, the more force she applies to the fluid, causing it to stiffen.