Still thinking Geoff's eyebrows. If I was his infant I think my attention would be drawn to his high more active brow rather than the low brow. My attention is still drawn to his right side and I have to directly try and keep my attention on his left in order to see the difference. Otherwise all I see is his right.
His eyebrows remind me of the movement of this girl's hands. (Video has been taken down) Could the movements be explained by a common drive manifested with the delay in only the excitatory pathway through the corpus callosum? I don't really know. My thinking in this endeavor is not scientific or for that matter logical ( I hope it is) but it does arrive from the subjective experience of playing with my own movements and paying attention. I obviously could be very wrong.
PS Seen twice today where the eyebrow on the left is more engaged. Here's one
President Obama gif
I know the President is left handed but if I don't actually look for his left eyebrow I don't see the left eyebrow raise. My attention is normally drawn to the right eye and head nod.