Skilled thieves are able to apply brewed poisons to their weapons. Weapons that are poisoned in such a manner tend to be very effective at poisoning enemies, but the poison will wear off of the weapon quickly.
Skilled thieves are also able to clean off poisoned weapons.
Poison can also be applied to food and corpses. Anything that tries to eat the poisoned item will become very sick. Butchered meat can also be poisoned and fed to corpse-eaters.
As with all poison skills, the thief should have knowledge of poison handling in order to avoid poisoning himself.