The cave goblins are a practical sort, using materials more readily available underground than any that might require potential damage to their subterranean dwellings, such as mining. This crossbow is made from bones, traditionally of creatures found beneath the surface.
Zanik once used this crossbow to defeat a deadly spectre in the underworld. A being infused with some dread malign power, that threatened the denizens of Um. Normal weapons had no effect on the creature, yet for some reason the bone bolts fired by this crossbow were enough to unravel its material form, banishing it back to the darkness.