Given that "monstrous situation" also covers sudden attacks of all sorts, this is true. Indeed, most people, when confronted by a sudden, unprovoked verbal
assault are taken aback, and do not respond effectively. Aggressive/psychopathic people rely on this widespread tendency.
That said, I don't think Alak wasn't even organized enough mentally to cower effectively. As I recall he more or less fell over when the girl reared back on him, then lay there in shock. Good cowering would have been trying to crawl backwards on his elbows I think.
The scene may have just been executed badly by the director and actors though.
What almost invariably does make a difference is training and experience. In the girl's case, I think the dead older brother seems like the type to have given her some hand to hand combat time.
I noticed that Alak (have i been spelling that wrong?) did try to crawl backwards on his elbows but was too freaked out to be successful at it. He kept losing his balance and falling back down couple times partly cause he couldnt seem to tear his frightened gaze away from Christie and the monsters.
I get the distinct impression that Alak has been given a nice easy childhood by his parents with little responsibility given how Datak doesnt seem to have involved him in any of his shady cutthroat buissiness practices whereas the McCauley kids seem to have been put to work by their father helping with the mine or with running the household. I definitely agree that the dead older brother seemed the type to have given his sister some self defence training.