but instead of starting to coo and talk, present the baby with a “still face” that shows no emotion. Research suggests that the baby will vocalize at you and try to get you socially engaged. When you fail to respond, babies will then turn away from you and avert their gaze if you try to maintain eye contact. To prove to yourself that the baby found your still, unresponsive face disturbing, or at least unpleasant, come back in a few moments and go through your usual routine with the baby.
I think babies can recognize the subtler changes of a face that is less expressive like mine if that's typical of a caregiver.
