Ulysses leaves and another flame draws near, making strange muffled noises that Dante likens to the noises coming from a Sicilian bull: a torture device that is a brass bull within which someone place, with a fire underneath, until they are roasted alive and their screams, as they emerge from the bull's mouth, become unintelligible and sound like a bull's roaring.
Dante's strange simile between the soul and a torture victim draws a parallel between our world and the underworld. It also conveys the extreme suffering of the soul that he talks to. Despite this, the soul is able to form articulate speech.
The spirit begs Dante and Virgil to speak with him. He asks about Romagna, a region of Italy. Virgil encourages Dante to talk to this spirit, who is clearly Italian. Dante tells the spirit that Romagna never has absolute peace and stability but that when he left the region last there was no open strife there. He gives news of individual cities, and then asks the spirit his name, so that his name can live on, on earth.
Dante offers to carry on the sinner's name on earth, in exchange for their conversation. Even in the depths of hell, the sinner's main concern is his homeland back on earth.
The spirit says that Dante will never carry his name to earth, since no one can escape from hell, and so he tells Dante about his life. (From his life story, he is identifiable as Guido da Montefeltro, though he doesn't state his name.) He says that he was a cunning and deceitful soldier, a Ghibelline, who realized that his deceit was wicked, had a religious conversion, and then became a Franciscan friar. But Pope Boniface VIII sought him out as a military adviser in his battles against the Ghibelline.
Guido is unaware of Dante's ability to travel through both earth and the afterlife. He doesn't realize that Dante actually can ensure that his name will live on, and seems only willing to share his story because he thinks it won't get shared.
Guido was hesitant to help, but Pope Boniface promised to absolve him of his sins ahead of time if he would help him destroy his enemies. Guido accepted the absolution, then, thinking himself protected, advised the pope with false counsel and the pope's attack on the Ghibelline's failed. When he died, St. Francis came to save him, but a devil took him to hell instead based on the argument that a man can't be absolved for a sin before he commits it, because one can only be absolved if one is repentant and one can only be repentant if one has sinned first. Once brought to hell, Minos sent Guido here to the eighth circle of hell, for his fraudulence and deceit. Having told his story, Guido leaves, lamenting his fate. Dante and Virgil go onward toward the ninth trench of this circle of hell.
The Church was in the practice of selling things like indulgences or otherwise granting pre-emptive absolution. Here Dante makes a logical argument—based on Aristotelian principles—that one cannot be granted absolution beforehand because if one is absolved and then sins, then by definition that person still intends to sin even as he is being absolved, and one can only be absolved if one is repenting the sin. By making such an argument Dante thereby asserts that reason and logic must inform moral choices and that Church authority, while sacred, can't operate without logic. Indeed, all of hell is profoundly logical, furthering Dante's argument that there is a logic to Christian spiritual thought and practice that can't be overruled, even by a pope.