Beaver's Tooth (3.5e Equipment)
From D&D Wiki
The handle of this +1 cold iron dagger is worked in the shape of a beaver, its curved blade exiting the animal's mouth like a single tooth. Its dissonance with lumber allows it to ignore the hardness of anything constructed of wood including weapons and doors. Attacks made with this weapon ignore the AC bonus of shields and armor constructed of wood. Anything enhanced by an ironwood spell is affected as well.