A guy out in Wyoming did it with no knife, back in the 70s or 80s, I forget. He happened upon a big grizz who had already been agitated by some hikers IIRC; instead of running he went on the offensive with his own fucking teeth. He clamped down on the bear's jugular and held on for dear life, until the bear passed out. Then it was branch + skull, until soft.
No steel of any kind involved, as far as I know. How big are those balls? I heard about this guy years ago and it still amazes me every time I think of it.