Erevan did his research once he was out of the pool and had eaten lunch and was surprised by what he found. It seemed that he had discovered a sense of aesthetics, which shouldn't be possible considering what he was.
Then again, there were a lot of things that shouldn't have been possible. Namely loving Molly in the first place.
Playing human for so long had practically turned him into one after all. Perplexing as this was, wasn't it a good thing? Not going through the motions as much would be nice.
The feeling usually happened when she was smiling at him and he had long found that pleasant but over time it had developed into something more. Based on his research, he thought her smile was beautiful.
But her smile hadn't been the only thing that made him feel that way so he must think she was beautiful in general. How had he not realized this before? It would have saved him a lot of trouble.