How to describe him?  He's entering a really great phase: alert, curious, and adorable.  He is frequently laughing, frequently gazing in wonder with wide eyes at everything around him.  He soaks it all in.  The flapping arms, the way he holds them horizontal and then suddenly flaps them down when he gets excited.

He used to get nervous and scared standing up.  he was kind of terrified and fascinated by it, and after a few minutes he would start to cry.  now he wants to stay standing all day long.  he gets standing up and suddenly the little head starts swiveling left and right, like hey now i can see things.  and sure enough there he is looking at the coffee table with the new Atlantic on it.

The way he watches first and then reacts.  There's this tiny moment between when you do the funny thing (make a sound, zoom your head toward him) and he reacts to it.  The reaction might just be a smile, or a gurgle, or it might be a full on laugh.  But he is clearly taking a few seconds to process whatever you're doing, take it in and chew on it, before he decides that he likes it and gives you his reaction. 

The quiet moments.  He can spend tens of minutes at a time just sitting quietly staring into space now.  That almost never happens if he's sitting in a car seat or on the couch.  But if I have him tucked under my arm--- and he's still just under the weight and height limit to fit under my arm--- he will sometimes just sit silently, sucking on his fist and slobbering all down his front.  This is much more likely to happen if I am active, getting up walking around and performing tasks.  He can be completely calm for a long time under the left arm, if he's watching me go about my business with my right arm.