In October 1960, Jane Goodall observed the use of tools among chimpanzees. Recent research indicates that chimpanzees' use of stone tools dates back at least 4,300 years (about 2,300 BC). One example of chimpanzee tool usage behavior includes the use of a large stick as a tool to dig into termite mounds, and the subsequent use of a small stick altered into a tool that is used to "fish" the termites out of the mound. Chimpanzees are also known to use smaller stones as hammers and a large one as an anvil in order to break open nuts.