But then you'd have to assume that furries and/or anthro stuff ARE animals, which is probably astep too far. Though they have animal characteristics, they are anthropomorphic (thus, anthro as slang), and, since the great majority of the time, they are sentient (along the line as humans), they'd be no more than a 2 on a 1-5 consensual scale.
As for rape, this is why intent modifiers come into play. If the intent, and the intent of the other, is to satisfy a rape fetish, then it's less "weird" than if either of their intents were malicious(then it's criminal, but certainly possible to satisfy one person's fetish). If either one of them are nonconsenting(thus making it the heinous crime), I would put it at the highest part of the scale -- a 10, or a 5N.
Doing it this way allows me to put everything in graph form.