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"The Spaghetti Catalyst" is the twentieth episode of the third season of the American sitcom The Big Bang Theory. This episode first aired on Monday, May 3, 2010.


Sheldon has a hard time trying to be friends with Penny after her breakup with Leonard. Later, Leonard and Penny decide to still be friends and are acting like divorced_parents|divorced parents when it comes to Sheldon.

Extended Plot[]

The Spaghetti Catalyst - Sheldon and Penny meet in the hallway

With little pieces of hot dog?

The Spaghetti Catalyst - The group

Thank you, Penny!

Leonard and Penny are still fresh from their break-up, and it is time for the guys to "pick sides" about who will remain friends. Sheldon, as usual, is oblivious to this social convention and keeps contact with Penny, going as far as inviting himself over for spaghetti (with cut-up hot dogs reminiscent of his mother). When Sheldon reveals to the guys how he's been talking to Penny, Howard explains to him how he cannot maintain friendship with both her and Leonard.

In order not to arise suspicions, Sheldon eats at his apartment, then sneaks off to the refrigerator to grab a pack of hot dogs to take over to Penny's place. Just as he's about to leave with the excuse of taking a walk; however, Howard leaves as well, insisting that the two go down together. Sheldon tries to shake off Howard, but ends up accompanying him right to his parked scooter. When he finally gets rid of his friend, Sheldon bumps into a dog which smells the hot dogs, and has to run for his life. He manages to shake the dog off and arrives at Penny's in a state of disgrace and holding a single hot dog. The two eat spaghetti together, and Sheldon ends up with a stomach ache from eating too much.

Sheldon has trouble keeping his friendship with Penny secret from his roommate, and ends up recounting his continued friendship to Leonard in the middle of the night. Leonard, however, seems not to care about this relationship. Sometime later, Penny and Leonard bump into each other in the laundry room, where the two try to keep things friendly between each other. Leonard explains how he's fine with Sheldon and Penny being friends, but seems upset when he learns that Penny is taking Sheldon for sheets, shoes and to a trip to Disneyland. Leonard gives Penny suggestions on how to take care of Sheldon at Disneyland, as he is familiar with the events of Sheldon eating junk food and throwing it up after he goes on Space Mountain, and is scared of Goofy, but alright with Pluto.

The remainder of this episode showcases Leonard and Penny as "separated parents" to their "son" Sheldon. Penny, it seems, has ignored Leonard's tips and Sheldon reacts exactly as Leonard had predicted. The two see Sheldon off to bed, and Penny admits to Leonard how they can remain friends despite their break-up. Leonard offhandedly tries to suggest they remain "friends with benefits". Sheldon is then having nightmares about Goofy after they leave.



  • "At least the issue of Leonard and Penny hanging out is fully addressed here. You can imagine a scenario where they would use Sheldon as an excuse to cover the awkward moments in conversation...Again the writers just have no interest in characterization and would rather have Sheldon camp his way through silly lie after silly lie. It's no more than should have been expected though, Penny and Leonard's relationship received no attention when they were together so why should it once they break up?...A one-dimensional episode from a show in danger of becoming one-dimensional." - The TV Critic's Review
  • IMDb user reviews


  • Title Reference: Sheldon's spaghetti dinner with Penny is the catalyst for repairing Leonard and Penny's friendship.
  • Chuck Lorre's vanity card [1]
  • This episode was watched by 11.63 million people with a rating of 4.6 (adults 18–49).
  • This episode aired in Canada on May 3, 2010, with 1.87 million viewers and a weekly ranking of #12.
  • Episode transcript [2]

Costume Notes[]

Violet Lantern

BDG Toxic Stripes

With her waitress uniform, Penny wears her Truly Madly Deeply Celestial Printed Hoodie (discontinued by Urban Outfitters), and in the laundry room, she wears Lucky Brand Clinched Floral Crop Pants, and burgundy red Ugg boots. During dinner with Sheldon, she wears a grey Nebraska Cornhuskers t-shirt. After the trip, she wears a Mickey peace sign hoodie from Disneyland.


  • Fourth appearance of the board game "Talisman: The Magical Quest Game, 4th Edition," following the episodes "The Peanut Reaction" (S1E16), "The Tangerine Factor" (S1E17) and "The Financial Permeability" (S2E14).
  • Sheldon is afraid of the Disney dog Goofy, but is alright with Pluto.
  • Sheldon doesn't complain about the tangerine chicken in this episode, unlike in "The Tangerine Factor" (S1E17).
  • The T-shirt with the star burst pattern that Sheldon wears is the Star Sapphire shirt from the Green Lantern series. The Star Sapphires preside over the emotion of love, reflecting Sheldon's split affections for Penny and Leonard.
  • On the door of the apartment on the second floor is a sticker with the word 'ACK' on it, which is a reference to the previous episode. In "The Wheaton Recurrence" (S3E19), Sheldon offers Penny ice cream, because he read in a Cathy comic book that when Cathy was upset she would eat ice cream after she had said the word ACK.
  • Leonard and Penny think that they can remain friends.


Sheldon: Go, Team Leonard!
(Holds a "L" on his forehead which typically stands for "loser")

Sheldon: Well, as my Meemaw would say, looks like we butchered a pig, but nobody wanted bacon. Oh and as for the tangent line; Sheldon and the hell hound, OR, How I lost my hot dogs.

Sheldon: (knock, knock, knock) Penny, (knock, knock, knock) Penny. (Long pause, knock, knock, knock) Penny. (Penny opens door, and a disheveled Sheldon is holding up one hot dog.) Here. I had to trade the others for my life.

Raj: Hey, do you think the elastic woman in The Incredibles (Helen Parr) needs to use birth control or can she just be a diaphragm?
Howard: (pauses for a beat) Well, that’s it. We’re officially out of things to talk about.

(Penny and a yawning Sheldon enter the apartment. Sheldon is wearing an embroidered Mickey ears hat.)

Penny: We're home.
Leonard: It's 10 o'clock; where have you been?
Sheldon: We stayed for the California Adventure water show. (World of Color) It was pure Disney magic.
Leonard: (to Penny) I was going to see that with him.
Penny: How was I supposed to know that?
Sheldon: It's alright. I'll see it again with you.
Leonard: And I have food here; you said you were going to call.
Penny: I know, I know.
Sheldon: I can still eat.
Penny: No, you already threw up once. Go put on your PJs, and brush your teeth. (points down the hall with authority)
Sheldon: (uncomfortable) Okay. Just don't fight.
Leonard: We're not fighting.
Penny: Just go.

(Sheldon heads for the hall)

Leonard: Aren't you going to thank Penny for taking you to Disneyland?
Sheldon: (child-like tone, with a smile) Thank you, Penny.
Penny: (smiles back) You're welcome, sweetie.

(Sheldon leaves)

Leonard: Want a cup of coffee?
Penny: (surprised by his offer) Oh, um, I should probably get going.
Leonard: (gently insistent) Come on; it's just a cup of coffee.
Penny: Yep, okay.

(They walk to the island, as Raj and Howard watch in awe. Raj whispers to Howard)

Howard: Oh, yeah, the whole thing seems a little twisted to me, too.
Leonard: (confused) What am I smelling?
Penny: (embarrassed) Sheldon's churro on my shoes.

(Scene: Sheldon's bedroom. Penny and Leonard are watching over him like parents to their child)

Penny: (wistfully) He's such an angel when he's asleep.
Leonard: (wistfully as well) Yeah. Shame he has to wake up.
Penny: (is quiet, then turns to Leonard) I think we can do it.
Leonard: (proudly) Smother Sheldon in his sleep? Wouldn't that be wrong?
Penny: No, be friends. You and me.
Leonard: Oh. Sure. Absolutely.
Penny: Good. I'm glad.
Leonard: Here's an idea. I'm just throwing it out there; friends who have sex.
Penny: (amused) Goodnight, Leonard. (walk out in the hall)
Leonard: (follows Penny) Kidding. Just a couple of friends goofin' around. (closes the door)
Sheldon: (tossing and turning in his sleep) No, Goofy, no...