Fish scale the surface, interacting only with the riblet tips, not causing any high-veloctiy flow in the valleys. Since this high velocity flow now only interacts with the riblet-tip, which is a very small surface area, the momentum transfer which causes drag is now much lower than before, thereby effectively reducing drag. Also, this reduces the cross-stream velocity fluctuations, which aids in momentum transfer too. The rough, sandpaper-like texture of shark and ray skin, coupled with its toughness, has led it to be valued as a source of rawhide leather, called shagreen. One of the many historical applications of shark shagreen was
Lampshades made from human skin claims that the binding of some ancient and medieval books may be made of human skin. Allegedly, a 13th-century bible and a text of the Decretals were bound in human skin. Along with this hearsay, there are reports of copies of the 1793 French Constitution being written on human skin and 19th-century anatomy textbooks being symbolically bound in skin. After the defeat of Nazi Germany, claims circulated that Ilse Koch, wife of the commandant of Buchenwald concentration camp, had possessed lampshades made of human skin, and had specifically tattooed prisoners killed in order to use their skin for this purpose.