Fly-by with a tangent, just cause...
Wash: That sounds like something out of science-fiction.
ZoŽ: We live in a spaceship, dear.
That's not a funny line, to me. Or at least, not from Wash's point of view. He's perfectly correct to make the distinction - a spaceship is not science fiction to him. It's science fact
. They live in it every day, it's a basic accepted part of their world. There's nothing fantastical about it, it's standard engineering, nuts and bolts that he can go and look at and play with and drive around.
Psychic teenage girls are not a basic part of their world, it's not anything that has a logical A-to-B comprehensibility, hence him seeing it as science fiction. I feel like people make fun of Wash for being stupid over that line, when it's actually perfectly sensible.
And that's how you get way too serious about what was supposed to be a comic line.