A crysknife is a knife whose blade is made from the tooth of a dead sandworm of Arrakis. To the Fremen, the crysknife is sacred, and they maintain much tradition around it. If it is drawn, it could not be resheathed until it had drawn blood. The sharpness of a crysknife is unparalleled. It is usually perceived to glow with a dull light. They averaged 20 cm in length.