^ I did see your comment earlier, but I'm not so sure. That same color of gray continues most of the way down the front edge of the handle and looks as if it may simply be a reflection of whatever gray material the prop was sitting on when photographed.
I think I'm going to stick with "it's not clear to me yet just what or where the trigger might be," for the time being. If we get a look from a different angle than this one, the trigger may be easier to spot. Pretty sure the thumb button on the grip's not it, though -- that doesn't seem very practical as a trigger, but it could be a safety of some sort.