The action is very symmetrical. They react in very much the same way, at very much the same time (yes, I know they're reacting to a sudden, violent event), and at very much the same speed. For each character, left and right arms move in very similar ways.
I would suggest making the reaction faster, make them duck more or less to one side or another, and by different amounts. Some extreme facial reaction would help too - wincing, perhaps. Hope that helps.
Stuart, who can critise animation far better than he can create it.