Bernadette: When's he coming?
Penny: Uh, he gets in on Sunday, and Monday morning, I'm gonna give him a tour of the labs and offices.
Sheldon: Oh. He gets in on Sunday, April first? (chuckles) Nice try, Penny.
Penny: What're you talking about?
Sheldon: April Fools' Day. This is another one of your classic pranks you try to pull on me every year.
Penny: Literally never pulled a prank on you.
Sheldon: Oh, really? What about last year, when you sent me that e-mail with the photo attached, but you didn't attach a photo.
Penny: That was a mistake.
Sheldon: Messing with me? Yes, it was. And this year, I am not falling for it.