The centaur leaves them on the farther shore of the river of boiling blood, and they set out through a strange, barren woods of trees with dingy leaves and poisonous thorns, where Harpies, half human, half bird, lament. This is the second round, Virgil tells Dante. Dante hears wailing but sees no one and is bewildered. Virgil tells him to break off a twig from one of the trees; immediately blood and a voice come out of the wound, asking why Dante is adding to his torment. The speaker turns out to be a famous statesman and poet named Pier delle Vigne, who had served an emperor and been imprisoned on charges of treachery. He killed himself in despair. Now he explains that he had never betrayed his master, and is glad to think that Dante will tell the truth about him when he returns to the world of living souls. He tells how those who have been violent against their own bodies here become thorn trees, and even at the Last Judgment will not again enter their bodies-only each dead body will be hung on the tree of the soul who threw it away. Then crashing through the woods, wounding all the trees on their way, come two of those here punished for wantonly throwing away all their own goods and destroying their lives that way, pursued by great black hounds who tear them apart.
Those in this strange and eerie wood re-suffer the violence they inflicted on themselves forever. Much as Dante admired and pitied Pier delle Vigne, he did not feel he could show him as being spared the fate he had chosen when he killed himself, so the story goes, by dashing his head against the wall of his cell.
The Inferno: Novel Summary: Canto 13