application is highly favoured within the body, as it allows the viscosity of blood to decrease with increased shear strain rate. Bingham plastic Fluids that have a linear shear stress/shear strain relationship but require a finite yield stress before they begin to flow (the plot of shear stress against shear strain does not pass through the origin) are called Bingham plastics. Several examples are clay suspensions, drilling mud, toothpaste, mayonnaise, chocolate, and mustard. The surface of a Bingham plastic can hold peaks when it is still. By contrast Newtonian fluids have flat featureless surfaces when still. Rheopectic or anti-thixotropic There are also fluids whose strain rate is a function of time. Fluids that require a gradually increasing shear stress to maintain a constant strain rate are referred to as rheopectic. An opposite case of this is a fluid that thins out with time and requires a decreasing stress to maintain a constant strain rate (thixotropic). Examples Many common substances exhibit non-Newtonian flows. These include: Soap solutions, cosmetics, and toothpaste Food such as butter, cheese, jam, mayonnaise, soup, taffy, and yogurt Natural substances such as magma, lava, gums, honey, and extracts such as vanilla extract Biological fluids such as blood, saliva, semen, mucus, and synovial fluid Slurries such as cement slurry and paper pulp, emulsions such as mayonnaise, and some kinds of dispersions Oobleck An inexpensive, non-toxic example of a non-Newtonian fluid is a suspension of starch (e.g., cornstarch/cornflour) in water, sometimes called "oobleck", "ooze", or "magic mud" (1 part of water to 1.5–2 parts of corn starch). The name "oobleck" is derived from the Dr. Seuss book Bartholomew and the Oobleck. Because of its dilatant properties, oobleck is often used in demonstrations that exhibit its unusual behavior. A person may walk on a large tub of oobleck without sinking due to its shear thickening properties, as long as the individual moves quickly enough to provide enough force with each step to cause the thickening. Also, if oobleck is placed on a large subwoofer driven at a sufficiently high volume, it will thicken and form standing waves in response to low frequency sound waves from the speaker. If a person were to punch or hit oobleck, it would thicken and act like a solid. After the blow, the oobleck will go back to its thin liquid-like state. Flubber (slime) Flubber, also commonly known as slime, is a non-Newtonian fluid, easily made