Paleolithic people used stone tools. Sometimes a stone tool was just a rock. It might have been useful for smashing a shell or an animal's skull, or for grinding grain on another rock. Other tools were made by breaking rocks to make a sharp edge. The next development in stone tool making was to chip all the edges of a rock so that it made a pointed shape, useful for a spearhead, or arrow tip. Some stone tools are carefully "flaked" at the edges to make them sharp, and symmetrically shaped. Paleolithic people also used tools of wood and bone. They probably also used leather and vegetable fibers but these have not lasted from that time. Paleolithic people also knew how to make fire which they used for warmth and cooking.