What I'm saying is the video did not show conclusively that it is exactly because of the still face. There were 2 elements in play in the experiment: the still

What I'm saying is the video did not show conclusively that it is exactly because of the still face. There were 2 elements in play in the experiment: the still face and the mother not moving at all. If the mom was moving instead but with a still face and the baby reacted the same way, then it is because of the still face. gsk, however, attested that it is the still face (see his reply to my comment above).