Two souls near Dante speak across him to each other: Guido del Duca of Romagna and Rinieri da Calboli of Forlì. Guido asks Dante who he is and where he's from. Dante enigmatically describes the Arno river without naming it — it begins in a mountain and flows to the sea; who comes from there? Guido picks up the cue and delivers a blistering condemnation of every city along the Arno valley. In the Casentino, people behave like swine (bestial appetite). In Arezzo, mongrel curs snapping. In Florence, wolves. In Pisa, foxes so full of fraud no trap can hold them. The metaphor of humans degenerating into animals resonates with Dante's broader moral vision from the Inferno — sin as a loss of humanity.
Rinieri then laments the degeneration of Romagna specifically — his own homeland, once full of great souls and noble lineages, now devoid of virtue. The catalogue of lost families (Traversari, Anastagi, Lizio, Arrigo Mainardi, Pier Traversaro) is an elegiac roster of a world that no longer exists. He also prophesies bitterly that Rinieri's own grandson Fulcieri da Calboli will become a brutal tyrant in Florence.
As they leave the terrace, voices thunder through the air — the examples of envy punished: Cain crying "Whoever finds me shall slay me" (Genesis's first murderer, consumed by envy of Abel's acceptance); and Aglauros, daughter of Cecrops of Athens, turned to stone by Mercury for envying her sister Herse's love affair with the god. The examples rush past like arrows and are gone. Dante reflects: why does the world keep hooking its heart on things that cannot be shared? Heaven has room for everyone; envy's logic — that another's gain is my loss — is cosmologically false. Grace is not a finite resource.