Soldier walk a certain way--they have a posture and gait defined by what they are. And spies are much the same way, except that their patterns are entirely different. Clint walks so that his feet don't make a sound, and he doesn't stand straight--he hunches as though he's ready to tuck and roll at any moment. When they enter the girls' room, he finds himself a corner, folds his hands behind his back, and observes.

And then they ask more questions and catch him off-guard yet again.

"Well, to be fair, I always just thought of it as the present." He's never been one to talk down to children, and duplicity isn't in his nature. So he answers honestly.