When Ethan was little, he exhibited deep concentration by crinkling up his nose.  Drew, on the other hand, pushes out his lips like this:
I witnessed Drew's signature expression this week as he pushed the kid cart at Trader Joe's (grocery store) for the first time.   When I gave him the cart, he knew just what to do:  He puckered out his front lip, pushed the cart over to the shelves, started pointing to food and babbling, and chose several choice items to put in his cart (I was impressed by is good taste, as he picked out brioche rolls, Irish cheddar, and pecans.)  He was doing well till we got closer to the speakers, at which point he abandoned his cart, pointed up at the music, and started dancing (waving arms and slowly lifting one leg at a time).  I couldn't get him to focus on his cart again after that . . . But, he did charm all of our fellow shoppers, who stopped to watch. 

I recently read an article which propounds the idea that you can read people very easily by simply observing the subtle upturn or downturn of their lips when they think they are unobserved.  I haven't tested it out yet, but am going to be watching for unsuspecting experimentees when I get the chance.