Inferno Canto XXV (the Eighth Circle, Seventh Pouch: the Thieves)
As Vanni Fucci finishes speaking, he throws his fists up in figs against God—a gesture of blasphemy. There goes Dante’s respect for him.
Indeed, Dante claims that now he considers the torturous serpents his friends.
As if in response, one snake coils around Vanni’s neck to shut him up. Then his buddies join him in wrapping Vanni up so completely that he can’t move.
Dante is so disgusted by Vanni’s behavior that he wishes Pistoia (Vanni’s hometown) would just destroy itself. Even Capaneus’s behavior cannot compare in its atrocity to Vanni’s.
As Vanni flees, he is immediately replaced by a centaur whose backside is covered in writhing snakes. But that’s not all: his human parts, his head and torso, are tortured by a mini-dragon who sets his skin aflame.
Just as we’re all wondering what this guy could’ve possibly done to get such a horrible punishment, Virgil tells us. Apparently, the centaur is called Cacus. Unlike his violent brothers, Cacus stole cattle from the herd of Hercules and thus was punished by having Hercules beat him to death. (In fact, Dante tells us Hercules administered one hundred blows with his club, but Cacus had already died by the tenth.)
As Virgil’s explaining these details, Cacus passes beneath them and immediately after him follow three nude souls.
But Dante is so preoccupied counting Hercules’s blows that he doesn’t notice them until one cries out, "Who are you?" It is ambiguous to whom this question is directed, because it never gets answered.
It has only the effect of bringing Dante and Virgil to attention.
Dante doesn’t recognize them but they luck out when one calls the name of another, asking where Ciafna is.
Right on cue, Ciafna leaps out. But it’s not what we expect; instead of a human being, it is a serpent with six legs… so more like giant, vicious caterpillar.
Ciafna pounces on the man who called him, gripping his limbs with its many legs while savaging the man’s face with its jaws.
As if that weren’t scary enough, predator and prey now begin melding together, exchanging color and shape. Dante compares their icky amorphous shape to that of a newly-lit paper which is just beginning to lose its color.
The two creatures now stare at each other and wonder aloud at the transformation. Here, we find out that the man’s name is Agnello.
Dante continues with a really sickening description of their union. Their two heads melt together, their limbs grow and twist together, and basically the final product is this hideous, totally alien figure that is not quite man but not quite snake either.
Another little serpent flashes by and attacks one of the two bystanders, piercing him straight through the navel.
But the impaled sinner doesn’t react at all. In fact, he only yawns.
They stare at each other, snake and man. And dramatically, their bodies begin smoking.
At this point, Dante is in full poet mode. He grosses us out. Now he tells the other famous Classical poets that they cannot match Dante in describing snake attacks or magical transformations.
Back to the repulsive transformation: within the smoke, the serpent’s tail divides into two while the sinner’s legs merge, the serpent’s skin grows soft while the sinner’s grows hard; the serpent sprouts limbs as the sinner loses his; the serpent grows hair as the sinner’s falls off.
The transformed serpent then stands upright and grows a face with ears, while the man, now prone on the ground, has his ears absorbed back into his head.
Finally, the man’s tongue becomes forked while the serpent’s becomes whole. In short, man and serpent have exchanged forms; one has become the other.
The man—now a snake—slithers off, hissing.
The man—who was a snake—now speaks. He names the man he attacked (the newly-formed snake) as Buoso and takes delight in his suffering.
Dante remarks on the freakiness of the transformations and is so distraught by them that his sight becomes blurred.
But that doesn’t stop him, as they’re all leaving, from recognizing the third sinner, the only one who didn’t undergo a gruesome transformation, as Puccio Sciancato, another thief.