Did you know that beginning sometime between 0-3 months, infants mimic facial expressions? I first came across this phenomenon (what seems like a million years ago) in college studying infant development. I have seen it mentioned in passing on parenting websites since then, but rarely is it shown just how cool it really is. I would love to video tape Lucie and Tim because they get really into the game, even trading coos and babbles.... yet I always seem to miss the moments they are doing the same thing at the same time!
Once baby is old enough to focus on your face, try opening your mouth and leave it there for a few seconds and wait to see what happens. Start with opening and closing and then add sticking out your tongue. It really works!