"And the leader made a trumpet of his ass."

---(Canto XXI, 219)

Is this an attempt at humor? Actually, I believe that this a departure from Dante's writing style. In the past 20 Cantos, the tone has been very sober. The book begins with a midlife crisis. People are being tortured for an eternity. There is not much fun to be found in hell. But, somehow, there is a hint of humor at the end of this Cantos. I thought that that was great.
I also thought that it was very fitting that it was a vulgar joke. What sort of joke would a fallen angel make? What would he do? He would fart, a very crude sort of humor. I also thought that this showed the Greek influences on Dante. The angel definitely has human properties. He farts, and he lies (next quote). This does not exactly fit with our modern idea of angels.

"Then, 'He who hooks the sinners, back that way,

Supplied a bad account of this,' he said."

---(Canto XXIII, 243)

A plot twist? What madness is this? Dante is pulling out all of the stops. Another radical departure: actual narrative. In the past 22 Cantos, the poem has been all about describing hell. This river is here, these people are there. Its basically a tour of hell. This does not make very good narrative, even if Virgil is your tour guide. Dante may have realized this. Or perhaps he just got bored. Whatever the reason, Dante has suddenly began injecting new elements to the inferno. Humor (albeit toilet humor) and Plot twists are the new additions. A demon deceives him! This conflict is not straightforward. It makes the narrative much more interesting, and moves moves the story along. I also find this ironic. Dante is adding these lighter, more story like elements into the poem at the deeper levels. These are the places where the truly sinful exist. This is where the most heinous of crimes are punished, where the tortures are most cruel. And yet, somehow, Dante chose this time and place to add plot twists and toilet humor?