The current issue of Blade magazine has a story about a gent that was attacked by a black bear and forced to kill it with a pocket folder (man is still the most dangerous animal).

Unprovoked attacks from black bears are comparatively very rare, but apparently this one had a broken jaw, was in bad shape, and driven to it by desperation and/or pain.

I think the moral may be that, no matter what we think we know about animals, there are always exceptions.