Cerberus was the three-headed dog guarding the gates of Hades.
In recent years he has been employed as the guardian of the tomb of the Twelve Flatheads.
Bivotar and Juranda had encountered an enormous 3-headed dog which was actually a puppy (perhaps a cerberus offspring); it was chained with a collar and its barking was so powerful that it collapsed the ceilibg behind, trapping them. The kids picked up and threw towards it a huge bone lying beyond its reach; it soon licked it clean and then, snapping its chain, ran toward the kids licking them and wagging its tail.