Now and then some trivial argument would break out, and one of them would kill another one, and all the others would detach themselves from the killer as neatly as blood clotting, and they’d consider the case and they’d either excuse him, for some reason, or else send him out to the forest to live by stealing from their outlying pens like a wounded fox. At times I would try to befriend the exile, at other times I would try to ignore him, but they were treacherous. In the end, I had to eat them. How is Grendel characterized in this excerpt?