Item from Dune by Frank Herbert
A sacred Fremen blade made from a sandworm's tooth — milky translucent, impossibly sharp, and bound by the deepest taboo: it must not be sheathed unblooded.
The crysknife changes every scene it enters. When a Fremen draws one, the stakes have escalated beyond negotiation. The blade represents the maker — the sandworm — which the Fremen consider sacred. To show a crysknife to an outsider is to accept them into the tribe or to mark them for death; there is no middle ground. In combat, the crysknife favors the slow, precise fighting style that Holtzman shields enforced on the Imperium — but wielded by Fremen who never used shields and therefore fight with a speed and ferocity that shield-trained fighters cannot match. The blade cuts through any unshielded material with trivial ease. The taboo is absolute: once drawn, the crysknife must taste blood before it is sheathed. This means every drawing is a commitment. Fremen do not brandish crysknives as threats. They draw them as promises.
Approximately 20 centimeters of curved blade, tapering to a needle point. The material is a sandworm tooth — milky white with an opalescent sheen that catches light in prismatic flashes. The edge is monomolecularly sharp when properly maintained. The hilt is wrapped in worm-leather, shaped to the owner's grip. Some crysknives are 'fixed' — treated to prevent disintegration — while others remain 'unfixed' and will dissolve if separated from a human's electrical field for too long.
Also known as: the maker's tooth, Fremen knife, the sacred blade