I came here to say the same thing. I had no idea he could smile. This is almost as important as learning of the Higgs boson.

I'm so glad you mentioned that, I wasn't going to watch it at first. A synopsis prepared by Hawking hours earlier read on command by his robot voice, all the while having the camera focused on him while he's shifting in his seat waiting for the statement to end, didn't interest me. But that smile at the end made my week.

Came to say this, ditto.