It should be fairly obvious where the fox' teeth have been. Cut those bits off and discard, eat the rest (cook thoroughly of course) - that's what I do. If in any doubt at all, don't eat it.
Like benkt, I've eaten duck breasts (and legs off Muscovies, they're big enough to be worth the trouble), and also chicken breasts. And made stock from carcases.
But then I eat roadkill if it was my car, or I saw it happen so know it's fresh when I collect it.