Ultimate Frisbee is a form of recreation practiced all over the world by the physically active segment of the population that enjoys running up and down a field repeatedly trying to get strangers to catch a flying toy. Tossing around a plastic disc acts as a mind narcotic, activating a dormant canine gene in their brains that induces them to chase and catch things. A variation of the game, which involves attaching sharpened blades to the frisbee, is called "krulling" the disc.