Leonard: Dr. Jeffries, hello again. Leonard Hofstadter.
Professor Proton: Oh, right. I remember your girlfriend. *Looking around* Is she here?

Sheldon: Sheldon Cooper does not cry.
Howard: That's true, you'd rust.

Professor Proton: Can I ask you a question?
Leonard: Yeah, sure.
Professor Proton: Why do you put up with Sheldon?
Leonard: Oh, you know because we're friends.
Professor Proton: Why?
Leonard: Wow, you ask really hard questions. Look, I know he can be aggravating, but what you have to remember is he's not doing it on purpose, it's just how he is. But he's also loyal and trustworthy and we have fun together.
Professor Proton: You know you're describing a dog?
Leonard: He did bite me once. But in his defense, I came up behind him while he was eating.
Professor Proton: They hate that.
Leonard: Sheldon is the smartest person I have met. He's a little broken and he needs me. And I guess I need him too.
Professor Proton: Why is that?
Leonard: Boy, you will not let this go, will you?

Sheldon: Arthur! Arthur, it's me, Sheldon Cooper.
Professor Proton: Trust me, I remember.
Sheldon: This is television legend, Arthur Jeffries. His science show inspired millions of children.
Professor Proton: Hold on, you have a girlfriend?
Amy: Yes, and I've heard so much about you. Hey look, we're wearing the orthopaedic shoes. I can't believe I dress like a celebrity.
Professor Proton: Okay, I get it now.