burr

The prickly seed case or flower head of certain plants — burdock, chestnut, cocklebur — designed to attach to the fur of passing animals and hitch a ride to new ground. A burr is a seed's transportation strategy: hooks, barbs, and spines that grip anything that brushes against them. Velcro was invented after a Swiss engineer examined burrs under a microscope and copied their hook structure. Also: the rough, raised edge left on metal after cutting, and the rolling r of a northern English or Scottish accent.