The Spaghetti Catalyst

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

Summary
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 when it comes to Sheldon.

Extended Plot
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. But Sheldon, as usual, is oblivious to this and keeps contact with Penny, going as far as inviting himself over for  (with cut-up  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. 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. When he finally gets rid of his friend, Sheldon bumps into a 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 stomachache 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. Some time 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. 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.

The remainder of this episode showcases Leonard and Penny as "" 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 off-handedly tries to suggest they remain "".

Critics
"At least the issue of Penny and Leonard 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 characterisation 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

Quotes
Sheldon: Go Team Leonard! (Holds a "L" on his forehead which typcially 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.

Trivia

 * This is the fourth appearance of the board game "Talisman: The Magical Quest Game, 4th Edition," following the episodes "The Peanut Reaction", "The Tangerine Factor" and "The Financial Permeability".
 * Sheldon is afraid of the Disney dog, but is alright with.
 * Sheldon doesn't complain about the tangerine chicken in this episode, unlike in "The Tangerine Factor".
 * The t-shirt with the starburst pattern that Sheldon wears is the shirt from the Green Lantern series. The Star Sapphires preside over the emotion of love, reflecting Sheldon's split affections for Penny and Leonard.