A Smouldering stone is a stone dropped by Cerberus and much more rarely, hellhounds. It can be used to upgrade the dragon axe, dragon harpoon, and dragon pickaxe into the infernal axe, infernal harpoon, and infernal pickaxe, respectively. These infernal tools have a 1/3 chance to instantly process and destroy a resource (granting half of the normal processing experience gained in Firemaking, Cooking, and Smithing, respectively).