In an oubliette, one man sits atop another, gnawing thru the skull to his brain. The cannibal is Count Ugolino; his victim a Pisan archbishop. The prelate accused Ugolino of treachery (evidently justly, since here the Count is!). But Ugolino focuses on how he was imprisoned with his sons; it's ambiguous but probable that he ate them to survive. Dante slides downward to Ptolomea, resting place of those who murder their guests. Faces upward, their tears freeze in their sockets! Here we learn that, the moment a person betrays, a devil overtakes its body & casts its soul into Hell.