Man, Tyler just never ceases to surprise with how much he understands, even if he can't verbalize it all yet.  After Kevin got the frame for Tyler's new play center erected, Tyler was having fun just walking around and around one of the legs of the framework.  I said to kevin "Wow, he is going to love this!  Look how much fun he is having just walking in circles around the leg!".  Tyler overheard me say this, looked up and started turning around in circles where he was standing!  I didn't even know that he knew what a circle was.  Amazing!