To create a crysknife in
nethack, you first need a worm tooth. A worm tooth can be obtained by killing a long worm. Once the worm tooth has been retrieved from the corpse, a scroll of
enchant weapon must be used to enchant the worm tooth to a crysknife. A cursed scroll of enchant weapon will change a crysknife back to a worm tooth.
If the crysknife leaves the inventory of a player or monster (for example, yanked from your hands by a bullwhip), the crysknife will revert back to a worm tooth.