The Irish Pub Formulation

The Irish Pub Formulation is the sixth episode of the fourth season of the CBS sitcom, The Big Bang Theory. This episode first aired in the United States and on CTV in Canada on October 28, 2010.

Summary
Leonard tries to hide from his friends that he's having a secret affair with Raj's sister, Priya. Sheldon gets involved and develops an elaborate cover story.

Extended Plot
Raj's sister Priya visits and inadvertently causes trouble for the friends. She and Leonard apparently have a history, despite Leonard's pinky swear with Howard that they would not hit on her in deference to Raj. They hook up during her layover in L.A., but are discovered by Sheldon, who devises an elaborate lie to cover it up involving an Irish bar and a pretty Irish barmaid; he even generates props to back-up his ruse. Leonard cannot persist in the deception and reveals his night with her. At first Raj is upset, but then calms down when Leonard said that he offered her his heart and she stomped on it. The guys then unleash confessions of all of the deceptions they have perpetrated on each other, including Sheldon's experiment feeding moth parts to Leonard mixed in his food. The episode ends with Sheldon preparing snow cones and serving one to Leonard, and confessing they were made with mangocaterpillar. Leonard then spits out the snow cone and leaves the apartment, upset.

Critics
"Bringing in family members is almost always a good idea in sit coms as it helps root that character in a real relationship we can all relate to. The writers did nothing with Priya but she may come back one day. Her leap over the couch to hide from Sheldon was a nice visual gag...Raj's sister comes to town, she sleeps with Leonard who is betraying Howard by doing so. Who was the plot focused primarily on though? Yes that's right, Sheldon ...Feed Sheldon . Feed Sheldon . Feed Sheldon ." - The TV Critic's Review

Quotes

 * Sheldon: You know I can't keep a secret!
 * Leonard: You can if you try. Think about it this way: if I were Batman and you were Alfred, you'd keep that secret, right?
 * Sheldon: Why do you get to be Batman ?
 * Leonard: Because the Batman has the secret.
 * Sheldon: Alfred has secrets, too!
 * Leonard: Like what?
 * Sheldon: Alfred knows that Barbara Gordon is Batgirl. Which I've now just told to Batman ! See, I cannot keep a secret!

Trivia

 * Penny does not appear nor is mentioned in this episode, as the writers wrote her out of this and the previous episode, after Kaley Cuoco, the actress who plays Penny, broke her leg in a horseback riding incident.
 * Thomas the Tank Engine was shown in Penny's apartment before but this is the first time it is referenced in the show.
 * Sheldon has athermodynamic fluctuations seminar the day after Priya spent the night with Leonard.
 * This episode introduces Priya Koothrappali and her dating Leonard.
 * In the car, Leonard says, "Okay fine, I’m, I’m a horrible human being, I’m the Darth Vader of Pasadena." He was compared to Darth Vader while likewise driving the car, in The Large Hadron Collision.
 * Sheldon retorts, "You’re far too short to be Darth Vader . At best you might be a turncoat Ewok." Darth Vader is 6'8" (2.03 m), an Ewok is about 3'3" (1 m), and Leonard  is 5'5" (1.65 m).


 * Leonard is 1/32nd Cherokee.
 * Sheldon seriously conceived an exaggeratedly complicated lie to cover Leonard, just like what he had done in The Loobenfeld Decay
 * Sheldon explains to Raj, "But that behavior is beyond the pale and cannot be tolerated. We are no longer friends." In The Friendship Algorithm, Sheldon similarly remarked to Raj , "Maintaining five friendships promises to be a Herculean task. So, I’m going to have to let one of you go. ... Raj, you’re out." In both instances, he almost immediately rescinded the decision.
 * It's as if Sheldon really did come with a manual (The Peanut Reaction), as Leonard is able to repeat Sheldon 's words about hating fun without even being present when he said it. Sheldon also made this evident in The Bozeman Reaction when he said on two occasions, "As you know, I’m not comfortable with prolonged good-byes and maudlin displays of emotion, so I prepared [a] short video."
 * Sheldon recalls April 12, 2005 at Bob's Big Boy, which was a Tuesday. This detail is consistent with his old schedule of going to Bob's Big Boy on Tuesdays as revealed in The Hamburger Postulate.
 * Despite Howard complaining about the cobbler, he continues eating it while Sheldon explains "Train Day".
 * The mythical Maggie's hair sample came from a lab orangatan.