It's the way he steps back and gazes up at her when she opens the door, isn't it? And she does look ravishing, so who could blame him for being smitten?

I'm not an expert on Oedipus, but I think the whole Sam/Ruth scenario is much more oedipal than the "normal" mother/son incest scenario: Even though he does know she is his mother, she is still younger than him, and she's hot, and these aren't attributes usually associated with one's mother.

Thank you! I'm glad it worked out.