Step dancing includes clog dancing in which the steps are performed by performers wearing clogs. They were usually worn with Cuban-heeled shoes, clogs, or Chelsea boots. Safety footwear now comes in many styles, including sneakers, clogs, and dress shoes. Under the long skirt was a pair of high-heeled clogs with some embroidery on them. The production of clogs (wooden shoes) was widespread in medieval Europe. The Asian clam clogs pipes and obstructs the flow of water in electrical generating facilities. The type of upper determines how the clogs are worn. Hydrilla crowds out native species, impedes irrigation, and clogs boat motors. Studies of non-human primates also show that social stress clogs arteries. The duckweed clogs the intakes on power boats, quickly causing them to overheat. When outside, oiran wore "koma geta" - three-pronged, 20cm tall pauwlonia wood clogs. Modern revivalist sides have tended more towards the wearing of clogs. After applying, residual glue soon clogs the needle, keeping moisture out. After using the glue, residual glue soon clogs the needle, keeping moisture out. Weary eventually succumbs to gangrene caused by wounds from the stiff clogs.