The Plimpton Stimulation

The Plimpton Stimulation is the twenty first episode of Big Bang Theory's third season.

Summary
Dr. Elizabeth Plimpton (Judy Greer), a cosmological physicist from Princeton University, comes to Caltech for a visit. Sheldon arranges her trip, and offers her to stay in his bed (with Sheldon sleeping on the sofa), rather than a hotel which he perceives as less hospitable. Leonard tries to impress her by talking to her about her work, but she's interested in having sex with Leonard, which he very much welcomes. The next morning, Sheldon is completely oblivious to what happened overnight, but Penny immediately detects what happened based on Leonard's and Elizabeth's body language, and becomes jealous, because she broke up with Leonard not too long ago. Later that day, at the Caltech cafeteria, Dr. Plimpton meets Raj and wants to bed him, too. That night, Howard and Leonard come to Raj's apartment for Halo night and find Elizabeth there, so she suggests sex with all 3 guys, but Raj manages to lock the other 2 out of the apartment and has sex with Elizabeth alone. At the end of the show, Leonard and Penny discuss whether or not he needs to explain to Penny what happened. Although Penny keeps insisting that he doesn't need to explain anything, Leonard explains that he had sex with Dr. Plimpton because "she let him".

Title reference: Dr. Elizabeth Plimpton comes to visit Sheldon for the purpose of science collaboration but winds up seducing the three other guys and having sex with Leonard and Raj.

Quotes
Elizabeth Plimpton: Do you like role-playing games?

Howard: Yeah, sure. In fact, I'm a dungeon master.

Elizabeth: Not tonight. Tonight, you are a delivery man. You brought soup, but, uh-oh, Raj and I don't have enough money to pay you. So we'll have to come to some other kind of arrangement.

Howard: Beg your pardon?

Elizabeth: You two figure out the details, I'm going to change into something I don't mind getting ripped off my milky flesh.

Howard: [after Elizabeth goes into another room] What the frak?

Raj: Go away. She wants New Delhi, not kosher deli. Besides, you have a girlfriend.

Howard: We broke up weeks ago.

Raj: Why didn't you say anything?

Howard: I was waiting for the right time. This is the right time.

Leonard: [arriving] Hey, who's ready for Halo?

Raj: Oh, this is like a nightmare. Get lost!

Howard: He's right. The numbers are shaky enough as it is.

Leonard: I don't understand.

Elizabeth: [peeking head through door] Oh, good. Leonard's here.

Raj: Good?!

Leonard: Elizabeth, what's going on?

Elizabeth: What's going on is you and Howard are my moving men and Raj is my new landlord and I don't have enough money to pay any of you. [goes back inside the room]

Leonard: Is she suggesting what I think she's suggesting?

Howard: Yep! Welcome to the Penthouse Forum.

Video
Video:The Big Bang Theory - Hilo