Leonard: What were you guys giggling about?
Penny: They were passing notes to each other.
Leonard: Oh-ho, love notes?
Penny: If you love math.
Sheldon: And we do.
Amy: It's for our super-asymmetry theory.
Sheldon: Yeah, Amy and I have been having so much fun collaborating together.
Penny: Well, you know what they say, you never collaborate as much as your first year of marriage.