In fact, I have no idea why Granger attacked Scabior so brutally whereas she almost casually killed Goyle. I just can't get the scene out of my head. Her distorted expression, her tight jaw, her dark eyes. The sight of her choking the bleeding man plays in a continuous loop in my mind's eye. And then that flicker in her gaze. As if this unexpected act of violence had given her back some lost peace for a brief moment.