However, this translator's explanation from the end of Canto I is already worth mentioning:
The gay Leopard is the image of the self-indulgent sins--Incontinence; the fierce Lion, of the violent sins--Bestiality; the She-Wolf of the malicious sins, which involve Fraud.
All right, I think I can agree that bestiality counts as a sin, but incontinence? Surely not. Messy, yes. Humiliating, yes, but not a sin. Even to call it "self indulgent" seems a trifle harsh.
[Okay, okay. If you really want to know, incontinent can mean "unchaste," but I'll be that's not the first thing you thought of either.]