This brainy fact will make you the sharpest knife in the drawer © iStock
Asked by: Lizzie Myers, Andover
The thinnest blades are three nanometres wide at the edge – 10 times sharper than a razor blade. These are made by flaking a long, thin sliver from a core of obsidian (volcanic glass). Obsidian knives have been tested for use as surgical scalpels but aren’t currently licensed for use on humans, since they could leave glass fragments in the wound.