Guess you'll just have to answer you're own question? Heh, unless I add a comment as well.

Curse your sudden and inevitably difficult question!

I think I'll have to go for, "Psychic though?" "We live in a spaceship, dear." "So?"

Because in the middle of the whole crew having a discussion, and about something serious, Wash and Zoe just have their own little moment, apart from everyone else. Because it's Wash being serious and Zoe not, rather than the other way around, and that might not be normal to everyone else but for them it is, that neither of them have to fill a specific role when they're around each other. Because it's Zoe reassuring Wash and him still being questioning. Because it's them and even though they're having their own little moment everyone stops to listen in. Love it.