I watched the first episode of the rerun of Ray Mears' Wild Food last night. In it Ray and Gordon Hillman visit Arnhemland to find out how Australian Aborigines went about searching for and preparing their food. Towards the end of the program their hostess is preparing a type of yam that needs soaking overnight to make it edible. She takes an empty snail shell, with a stick pokes a hole in its side, and then proceeds to use it to grate the yam into thin strips. Mears and and Hillman are quite impressed by the simplicity and effectiveness of this tool and they speculate that if such a shell turned up in an archaeological dig, it would be unlikely to be recognised as a tool.