When these bones are put on a pyre ship and burnt (requires a tinderbox, axe and any type of non-pyre log), they will summon a Barbarian spirit, who may thank you for putting his soul to rest with an item. The reward may be a dragon full helmet, various potions, runes or projectile ammunition. Many players will attempt killing mithril dragons in the hopes of obtaining a dragon full helmet drop; if unsuccessful, they can take any gained chewed bones to be burned in a pyre ship for another chance at gaining a dragon full helmet, however the chances of that are fairly rare. Note that using higher level logs does NOT increase chances of receiving a dragon full helm.