I'm only gonna post the gif and the comment, since it pretty much summed the entire scene up.
But just him saying “He sees me!”, then pausing trying to process the information. To be noticed, actually feel like he exists, the first time in 300 years. He almost looks afraid as well, as if this possibly couldn’t be happening to him. Afraid he’s imagining the entire thing and the moment could vanish instantly. Then his mouth twitches a smile as he realized this is really happening. All this in a few seconds of animation. It’s nearly over whelming emotionally as you think about it. The animators did such a wonderful job capturing the emotion and realization he gets as he says it again. “He sees me!”
I'm sorry for all this ROTG spam, but the movie was so good, I can't help it!