The Big Bang Theory (season 3)

The guys have returned home from their three-month expedition at the Magnetic North Pole (from the Season 2 finale). Penny finally reveals her feelings for Leonard by kissing him as soon as he goes over to her apartment to tell her he was back. Meanwhile, Howard and Raj reveal to Sheldon that they and Leonard tampered with his experiment on magnetic monopoles by using an electric can opener. Sheldon is distraught and angry with all of them as he had already submitted his results to the university. He is forced to make an apology, making him the butt of jokes from everyone at the university, particularly Kripke. Crushed that his best friends have destroyed his dreams and humiliated him, Sheldon returns to his home in Galveston, Texas. On Penny's advice, Leonard, Howard and Raj reluctantly go to Galveston to bring him back.

At his home, Sheldon is becoming increasingly annoyed with his mother's strict Christian lifestyle. When the guys come over and plead with Sheldon to come back to Pasadena, he initially refuses, but following an argument with his mother about evolution, he forgives them and returns to Pasadena. The episode ends with Penny and Leonard finally having sex, but both of them now feel their relationship got weird.

Recurring characters: Laurie Metcalf as Mary Cooper and John Ross Bowie as Barry Kripke

Leonard and Penny struggle to recover from a not-so-great first hookup and try to figure how to overcome their current problem. A romantic evening between the pair soon turns into a night filled with drunken sickness. The next day Penny talks to Sheldon regarding her current problem with Leonard and Sheldon points out that if things do not work out, they can always return to being friends. After Sheldon tells Leonard that he spoke to Penny about their problems, Leonard goes to Penny's apartment. Penny tells Leonard that being friends was much simpler and that it will take the pressure off, something that Leonard agrees to. They decide to go back to being friends, however it is clear that neither wants that and they soon give in to their attraction.

Meanwhile, Sheldon and Howard stake their most valuable comic books (Sheldon's "Flash of Two Worlds" against Howard's Fantastic Four #48) on a bet to determine the species of a cricket. Sheldon times the chirps and claims it is a snowy tree cricket, and Howard insists it is a common field cricket. Along with Raj, the three spend a long time locating the cricket. They settle the bet by taking "Toby" to Professor Crawley, Caltech's depressed entomologist, who has just lost funding for his lab. Howard is proven correct that it is a common field cricket, so Sheldon has to give up his copy of The Flash.

Guest star: Lewis Black as Professor Crawley

After a sexual encounter that results in Penny's bed breaking, Penny and Leonard end up sleeping in Leonard's room, much to Sheldon's dismay. Sheldon tries to condition Penny using chocolate, despite Leonard's opposition, rewarding her for what he considers to be correct behavior.

Howard and Raj go out to a goth club and meet two girls. After they say they would prefer to go "somewhere else and have some fun," the four end up in a tattoo shop, which makes Raj and Howard reveal their true selves and admit to not being goths (as well as having fake tattoo sleeves), missing their opportunity with the girls rather than get tattoos.

Note: Leonard, Sheldon, and Penny are watching the anime Oshikuru: Demon Samurai, which is a reference to a 2004 episode of Two and a Half Men ("The Salmon Under My Sweater") in which Charlie and Jake collaborate on the theme song to the same show. Both shows were co-created by Chuck Lorre.

Guest stars: Molly Morgan as Bethany, Sarah Buehler as Sarah and Andy Mackenzie as Skeeter

Raj's research on trans-Neptunian objects comes to a dead end and he faces deportation to India unless he gets a new job. After he is unsuccessful applying for other jobs at the university, Sheldon offers Raj a chance to work "for" him, rather than work "with" him. Raj reluctantly accepts Sheldon's offer. With Raj working for Sheldon for long hours, Howard feels lonely, so he tries to hang out with Leonard and Penny (even making them breakfast) but they tell him that they need to be alone together. Later, Sheldon and Raj disagree on how to solve a work-related problem and Raj walks out. Sheldon actually apologizes at the end of the episode and he accepts that Raj was right but does not concede to him being wrong. They agree to continue working together.

Guest stars: Elizabeth Bogush as Dr. Catherine Millstone and Oliver Muirhead as Professor Laughlin

Leonard reluctantly agrees to fulfill a pledge he made to Wolowitz years earlier, and asks Penny to set Wolowitz up with one of her friends, to which she agrees. They go on a double-date and Howard is introduced to Penny's friend Bernadette. Although it seems like they do not have anything in common, they start to get along well when they learn about each others' problems with their mothers.

Meanwhile, Sheldon enters a collectible card game tournament only after he hears that Wil Wheaton, for whom he harbors a deep resentment for missing a 1995 Sci-Fi convention, is also participating. With Raj as his partner, they reach the final match against Stuart and Wil Wheaton. Sheldon can easily win, but Wil lies, claiming his grandmother's death prevented him from appearing at said convention, which tugs at Sheldon's heart-strings. Sheldon lets Wil win, leaving Sheldon even more resentful of him after Wil tells him the truth that his grandmother is still alive.

Recurring characters: Wil Wheaton as himself, Kevin Sussman as Stuart Bloom and Melissa Rauch as Bernadette Rostenkowski
Note: This episode marks the first appearance of future regular cast member Melissa Rauch as Bernadette Rostenkowski and also marks the first cameo appearance of Wil Wheaton on the show.

Penny invites her friends over to her apartment to watch the Nebraska Cornhuskers football game that Saturday, but does not invite Leonard as he is not a football fan. Determined to fit in with his girlfriend's friends, Leonard decides to learn the rules of football from Sheldon, who is highly knowledgeable about football having grown up in football-crazy Texas. With the knowledge he learnt from Sheldon, Leonard goes over on Saturday to watch the game. However his comments on the game are too clinical and he fails to fit in with Penny's friends. He later becomes bored of watching the game and leaves at half-time to fly kites with Sheldon.

Meanwhile, Raj falls out with Howard after the latter abandons him during a kite fight with Leonard and Sheldon to pursue a girl, as a result of which he loses his kite to Sheldon. Howard decides to make it up to him by spending an entire Saturday with him at the La Brea Tar Pits. However he fails to keep his promise and again abandons Raj at the tar pits to pursue another girl.

Guest stars: Zachary Abel as Todd and Jason Mesches as Denny

When Penny invites her guitarist ex-boyfriend Justin over to sleep on her couch, Leonard becomes upset. They start a fierce argument, which makes Sheldon upset as he is reminded of memories of his parents fighting. He later tries to convince Penny to make up with Leonard, but ends up telling her how Leonard dislikes her temper, which only makes her angrier. Upset with the constant bickering between the couple, Sheldon leaves Leonard's apartment. He tries to take refuge in Raj's apartment, but sees him arguing with his parents over webcam. Then he goes to Howard's house, but hears him and his mother bicker with each other. Leonard and Penny begin to search for Sheldon and eventually find him at the comic book store. They manage to convince Sheldon to come back to the apartment, but not before allowing him to buy a robot and a comic book. The episode ends with Justin sleeping on the couch in Leonard and Sheldon's apartment (with Sheldon sitting in his spot) and Leonard and Penny, having finally made up, sleeping together in Penny's apartment.

Recurring characters: Kevin Sussman as Stuart Bloom, Brian George as Dr. V.M. Koothrappali and Alice Amter as Mrs. Koothrappali

Sheldon investigates cries for help from across the hall: Penny has slipped in the shower and dislocated her shoulder. Sheldon is enlisted to get her to the hospital emergency room. Penny is neither dressed (yet) nor can she drive her car. Sheldon has to help Penny get dressed with his eyes closed. He inadvertently tries to put her breast in her sleeve. He has yet to drive a real car and his driving simulator experience was a disaster. The trip to the hospital is slow and Sheldon pushes Penny's rage closer and closer to the brink but they get there fine and, by the end of the episode, Penny (under the influence of strong analgesics) is rather happy with Sheldon's help. She gets him to sing Soft Kitty with her as a round.

Leonard is with Raj and Howard on a camping trip to watch the Leonid meteor shower but all three succumb to the effects of "magic" cookies they are given by Deadhead campers nearby. Firstly, Raj and Howard start to make fun of Leonard's American accent (which even Leonard makes fun of), while looking at the stars, waiting for the meteors. They then share a conversation about their secrets, Raj talked about what it would be like to be king of the rabbits (if he could speak the language of rabbits), Leonard thinks of changing his name to "Angelo" because his name has the word "nerd" in it and "Angelo" has "Angel" and "Jell-O" in it. Howard admits that he lost his virginity to his second cousin. The trio are starving and begin to run out of food; fortunately, Howard remembers that his mother packed food for him and shares it with Leonard and Raj. Hilarity ensues as their minds expand and the munchies set in and they forget about the meteor shower. The episode ends with Leonard and Raj making fun of Howard and his experience of sleeping with his second cousin.

After their third date, Howard's new girlfriend, Bernadette, asks him where their relationship is going. He avoids her for a week, thinking about whether he should "settle" for her or hold out for the dream of superstars like Megan Fox. After a dream in his tub involving a romantic-evening-turned-lecture from Katee Sackhoff, he decides that he should stick with reality. He proposes to Bernadette at The Cheesecake Factory, but gets rejected, and then sings her his version of the song "Bernadette" (by the Four Tops) in order to win back her affections; he succeeds when she declares it the most romantic thing anyone has ever done for her.

Meanwhile, Kripke severely embarrasses Sheldon on National Public Radio's talk show Science Friday by filling Sheldon's office with helium so that his voice is higher-pitched than usual. While at first pouting and accepting defeat, Sheldon is convinced by Leonard and Raj (who originally enjoyed the prank) to fight back. Sheldon takes vengeance on Kripke with an elaborate trap in which a massive cloud of gooey foam, set off by a human presence, falls through the false ceiling into Kripke's office, covering him in foam. However, the trick backfires on Sheldon when the visiting Caltech president and board of directors are also hit. Sheldon gives himself away with a pre-recorded video stating that he has sent the taped trick to YouTube, and proclaiming himself the mastermind. Leonard and Raj also share the consequences when Sheldon gives them their (now unwanted) share of the credit.

Recurring character: Melissa Rauch as Bernadette Rostenkowski, John Ross Bowie as Barry Kripke and Carol Ann Susi as Mrs. Wolowitz
Guest stars: Katee Sackhoff as herself and Ira Flatow as himself

Bernadette joins the guys and Penny for dinner and shows an interest in physics, particularly in the work that Leonard is conducting. Leonard offers her the chance to tour his lab and watch him conduct an experiment. Penny gets jealous because she does not have enough background in physics to talk to Leonard about his job. She then seeks out Sheldon to teach her physics. Initially refusing, Sheldon is persuaded by Penny to take on the challenge. Later, while they all have dinner in the apartment, Penny spouts off a prepared spiel which Sheldon has coached her in, expressing Sheldon's view that Leonard's experiment is functionally identical to one already conducted by a Dutch team of scientists.

Bernadette's interest in Leonard's work makes Howard jealous and he accuses Leonard of being interested in Bernadette. Leonard then texts Bernadette that, because Wolowitz is jealous, it might be a good idea to cancel the tour. Bernadette receives the text message right before she is going to have sex with Howard, who becomes enraged and subsequently storms out. The following day, as Howard confronts Leonard at his lab, Bernadette arrives to watch Leonard conduct the experiment, at which point Howard apologizes to her, and they kiss and make up.

Recurring characters: Melissa Rauch as Bernadette Rostenkowski and Carol Ann Susi as Mrs. Wolowitz

At Christmas, Leonard's mother visits a horrified Leonard and a delighted Sheldon. Penny is upset because Leonard did not tell her about his mother's visit, nor his mother about their relationship. This problem becomes secondary when Leonard learns that Sheldon has been in touch with his mother. Leonard is told about his parents' pending divorce, his mother's surgery, and the death of his dog, all of which Sheldon had known for weeks. Beverly questions Howard and Raj about what she views as their ersatz homosexual relationship [alluding to her last visit in The Maternal Capacitance]. Penny and Beverly go out drinking and become "home girl" buddies. When they get back to the apartment, an inebriated Beverly gives Sheldon a deep, long kiss (which they later agree to keep secret from Leonard), but Beverly remarks that she would prefer the busboy she saw at The Cheesecake Factory.

Recurring character: Christine Baranski as Dr. Beverly Hofstadter
Note: Christine Baranski was nominated for a Primetime Emmy Award for Outstanding Guest Actress in a Comedy Series.

Leonard and Penny's relationship hits an impasse when, while on a double-date with Howard and Bernadette, she reveals that she has taken career advice from a psychic, only for Leonard to laugh, infuriating her. Later, Howard tells Leonard that if he wants to be able to be in a relationship, he will have to accept that people will have differing beliefs. Leonard apologizes to Penny and agrees to visit her psychic, despite her having declined to read a book debunking psychics, remarking that "one of us has to keep an open mind."

Meanwhile, Sheldon and Raj attend a university mixer, with Sheldon as Raj's wingman. Sheldon only agrees because Raj bribes him with a Limited Edition Green Lantern lantern, which Sheldon subsequently carries with him to the mixer. They meet Abby, who takes a liking to Raj, and her friend Martha, who tries to connect with Sheldon. They end up playing Rock Band at Sheldon's place. For a second date, Raj bribes Sheldon with his pair of Hulk hands, signed by Stan Lee. After Sheldon announces that he is going to bed, Martha asks if she can stay in his room to avoid Raj and Abby, who are "getting busy". Sheldon obliges and immediately leaves to sleep in Leonard's room, leaving Martha alone.

Recurring character: Melissa Rauch as Bernadette Rostenkowski
Guest stars: Danica McKellar as Abby and Jen Drohan as Martha

Leonard and Sheldon return from dinner to find their apartment broken into, with their TV, laptop, hard drives, video game consoles and video games stolen. Sheldon fears being alone in the apartment due to the robbery, so he forces Leonard and Penny to stay in the apartment. The next day, Howard designs a state-of-the-art security system for the apartment using components he "borrowed" from the Department of Defense. However, after Sheldon himself is caught in the security system, he decides that the apartment is no longer safe and plans to leave Pasadena for a safer city. After rejecting Enid, Oklahoma, Boone, North Carolina and the entire state of Nebraska (because Penny is from there), he decides to move to Bozeman, Montana. But when Sheldon arrives there, he gets robbed again, so he returns to Pasadena.

Guest star: Julio Oscar Mechoso as Officer Hackett

Sheldon's search for the answer to a physics problem keeps him up for several days and he becomes obsessed with finding the answer. His obsession with solving the problem goes to the extent of visualizing food as atoms and even sneaking out in the middle of the night to go to the mall ball pit, forcing Leonard to rush to the mall and get him. He then decides that he needs a menial job to think better because Albert Einstein came up with the Theory of Relativity while working at a menial job at the Swiss patent office. Since the United States Patent and Trademark Office is in Washington DC, and he does not want to move out of Pasadena, Sheldon interviews for any menial job with the County of Los Angeles. At the county office, Sheldon angers the woman interviewing him, to the extent of her calling security to remove him. Sheldon then decides to work at the Cheesecake Factory with Penny as he considers her job the most menial of all. He shows up and works as a busboy and waiter without actually being hired or demanding pay, and turns out to be a more efficient waiter than Penny until he drops and breaks a tray of dishes. The scattering of the shattered pieces leads him to the answer to his problem, and he promptly walks out without cleaning up the mess.

Meanwhile Leonard, Penny, Howard, and Bernadette go to disco night at the roller skating rink where the guys embarrass their girlfriends with their outfits and dancing. Raj is left out as he does not have a girlfriend, even though it was his idea to go to the skating rink. Eventually Raj successfully pressures a reluctant Howard to take him to the skating rink.

Recurring character: Melissa Rauch as Bernadette Rostenkowski
Guest stars: Yeardley Smith as Sandy and Kevin Brief as Glenn

Leonard announces to the guys that a professor is unable to attend a conference in Switzerland and visit CERN's Large Hadron Collider, so he has been designated to be his replacement, and he gets to take one guest with him. Sheldon wants Leonard to take him to Switzerland because according to the Roommate Agreement, if one of the friends is ever invited to visit the Large Hadron Collider, the other friend should accompany him, however Leonard decides to take Penny with him as the trip would coincide with Valentine's Day, their first together as a couple. Sheldon is distraught and begins to constantly give signs indicating that Leonard "betrayed" him. He even gives Leonard breakfast in bed so that he would change his mind, but Leonard is firm on taking Penny. Sheldon later convinces Penny to drop out of the trip, but this does not go down well with Leonard, who angrily reiterates that he will never take him along, prompting him to terminate their friendship. But later that night Penny falls ill, so Leonard asks Sheldon to accompany him to Switzerland in Penny's place, but Sheldon too has fallen ill. As a result, Raj accompanies Leonard to Switzerland while Sheldon and Penny spend Valentine's Day together.

Stuart announces that Stan Lee is coming to the comic book store on Thursday to sign comic books, and the guys are very excited about the news. However on the same day, Sheldon has to appear in court in a case of running a red light when he was driving Penny to the hospital (in the episode "The Adhesive Duck Deficiency"), causing him to miss meeting Stan Lee. At court, Sheldon insults the judge and is imprisoned as a result. Later Sheldon apologizes to the judge and is freed, but he now nurses a grudge against Penny because she made him miss meeting Stan Lee. To make it up to him, Penny takes Sheldon to Stan Lee's house to meet him, but Stan, not impressed by their intrusion, sarcastically invites them in. Sheldon, who does not understand sarcasm, enters Stan's house, prompting him to call the police. The episode ends with Sheldon gleefully returning to his apartment with a restraining order from Stan and hanging it next to the restraining order from Leonard Nimoy.

Trivia: The judge's name is J. Kirby, a comic collaborator with Stan Lee.
Recurring character: Kevin Sussman as Stuart Bloom
Guest stars: Stan Lee as himself, Steve Paymer as Judge Kirby, and Marcus Folmar as Guard

The guys return to the apartment with a large box of random TV and movie collectibles from a garage sale, including a prop version of the One Ring. This turns out to be a prop made for The Lord of the Rings film trilogy, with high value to collectors, and the four promptly argue over who gets to keep it. Leonard eventually gives it to Penny for safekeeping. That night Sheldon sneaks into Leonard's room (where Penny is sleeping) and tries to steal the ring which she is wearing around her neck. She wakes up and punches Sheldon in the face. The next day in the cafeteria Howard, Raj, Sheldon, and Leonard all grab on to it. They decide whoever is the last one holding the ring will get to keep it. Leonard removes himself from contention when Penny shows him the contents of a bag she got from Victoria's Secret. Then Sheldon, Raj, and Howard all fall asleep and let go of the ring, and the next morning Leonard says he sent it back to the original owner, but he kept it hidden in his room. That night Sheldon tries to take the ring again and he and Leonard wrestle for it on Leonard's bed. The episode folds with Penny walking out of the room muttering to herself about how she should "go back to dating dumb guys from the gym."

Guest star: Frank Maharajh as Venkatesh Koothrappali
Note: This was the most watched episode of season 3, with 16.32 million viewers.

Sheldon is delighted when he wins a science award, but then tells the guys that he cannot accept it because of his fear of speaking to a public audience. Leonard, Raj and Penny offer to help Sheldon overcome his fear of speaking in public. Sheldon then christens himself, Leonard, Raj and Penny as the C-Men (Cooper-Men). All the C-Men fail to overcome Sheldon's fear; Raj tries to teach Sheldon meditation to calm his nerves, but when Raj tells Sheldon to think of a place where he feels at home as part of the meditation process, Sheldon instead imagines a Godzilla-like monster approaching his simulated city Sheldonopolis; Penny takes Sheldon to buy a new suit to give him confidence, but Sheldon is more interested in weird and fancy suits; Leonard attempts a psychotherapy session with Sheldon, but Leonard actually ends up having a nervous breakdown, after reminiscing a humiliating incident with his mother which happened when he was eight years old. As a last-ditch solution, Penny offers Sheldon alcohol. This solution actually works, but it makes Sheldon drunk and he speaks nonsense during the awards ceremony. At one point in his speech, Sheldon drunkenly removes his pants. When Sheldon wakes up the next morning, unaware of the events which happened the previous night, he sees his humiliating speech uploaded on YouTube.

Trivia: The song Sheldon sings at the ceremony is the song "The Elements" by Tom Lehrer.
Note: Jim Parsons won the Primetime Emmy Award for Outstanding Lead Actor in a Comedy Series for this episode.

After having sex, Leonard says "I love you" to Penny, but she only replies "Thank you", prompting both of them to start thinking about where their relationship is heading. The next night, Penny and the guys have a bowling match with Stuart and some of the comic book store regulars (with the loser to be publicly humiliated in a fashion to be chosen by the victor). As one of the guys in Stuart's team could not make it to the match, Stuart substitutes him with Wil Wheaton. Sheldon vows to get revenge for what Wheaton did to him in The Creepy Candy Coating Corollary. During the match, Leonard offers Penny chili cheese fries, to which she expresses her love of chili cheese fries. Angered that Penny could describe her feelings for food but not for him, Leonard starts a fierce argument with her, following which she leaves the bowling alley in a huff. Without Penny, the guys are forced to forfeit their match, which greatly upsets Sheldon. The next day, he makes Leonard and Penny talk and supposedly patch things up and then schedules a rematch that night. During the match, Wheaton tells Penny that he endured two years of misery with a girlfriend who could not say "I love you" to him. When it is Penny's turn to bowl, she feels that Leonard's encouragement is pressuring her and lashes out at him. At this point, she realizes that she just cannot say "I love you" to Leonard, prompting her to break up with him and storm out of the bowling alley. With Penny abandoning them again, the guys have to forfeit the match. Sheldon then confronts Wheaton, who reveals that he intentionally broke up the couple so that his team would win. The episode ends with the guys entering the comic book store dressed up as female superheroes which is Stuart's idea of publicly humiliating them for losing the match.

Recurring characters: Wil Wheaton as himself and Kevin Sussman as Stuart Bloom
Title reference: Wil Wheaton's return as a guest star on the show.

Leonard and Penny have broken up and are no longer talking to each other. Sheldon continues to maintain contact with Penny and invites himself over for a spaghetti dinner (with cut-up hot dogs reminiscent of his mother's cooking) at her apartment. When the guys find out that Sheldon is still being friends with Penny, Howard tells him that he cannot be friends with both Penny and Leonard. As a result, Sheldon hides his dinner plans and eats dinner with the guys. He then has dinner with Penny, but cannot keep his friendship with her secret, so he reveals to Leonard that he is still friends with Penny, which Leonard does not mind. The next day, Penny bumps into Leonard in the laundry room and tells him that she is taking Sheldon with her to Disneyland that Saturday. When she drops Sheldon home late on Saturday night and puts him to bed, she tells Leonard that they can remain friends despite their break up, which he accepts. However he suggests that they could have a friends with benefits relationship, which she refuses.

Dr. Elizabeth Plimpton, a cosmological physicist from Princeton University, accepts Sheldon's invitation to stay over the apartment during her visit to Cal Tech. She takes an immediate interest in Leonard, and the two end up sleeping together. The next morning, Penny, who recently broke up with Leonard, learns about their tryst and becomes jealous. Leonard assumes that he and Elizabeth are now an item, and shows her around, introducing her to his friends, including Raj and Howard. Later that night, Howard and Leonard go to Raj's apartment for Halo night and find that Elizabeth is there, and is trying to seduce Raj as well. When she sees that Howard and Leonard are present, she suggests role-playing sex with all three of them, much to the shock of the men. Raj manages to lock the other two out of the apartment, so he could be alone with Elizabeth. Back home, Leonard and Penny discuss whether or not he needs to explain to Penny what happened. Although Penny keeps insisting that he does not need to explain anything, Leonard explains that he had sex with Elizabeth because "she let him".

Guest star: Judy Greer as Dr. Elizabeth Plimpton

Leonard fights with Sheldon over the setting of the thermostat, then storms out of the apartment and visits Penny, who has been listening to the argument. He tells Penny that he should have known about Sheldon from their first meeting, and his exposition to Penny of their early days is presented as a series of flashbacks that occupy most of the episode.

The flashbacks begin in 2003, with Sheldon's departing former roommate's dramatic warning to Leonard, and the opinion of Louie/Louise, the transvestite male then occupying the apartment that Penny moves into in the first episode – that Sheldon is "crazy". Having found the apartment, Leonard meets Sheldon who poses, at the door, one question about the sixth noble gas (Radon) and another consisting of "Kirk or Picard?" before allowing him to enter and undergo further examination, and the ensuing rigorous interview questions and intrusive conditions suggest Sheldon's literalness, rigidity, egotism, and peculiar priorities.

A flashback includes Leonard's first encounter with Sheldon, and the acquisition of the lawn chair featuring what Sheldon calls "my spot".

Another flashback, introduced by Penny wondering why Leonard continues to live with Sheldon, reveals two events: Sheldon inadvertently kept Leonard from revealing a top secret rocket fuel to (the previously mentioned but unseen) Joyce Kim, a North Korean spy, by angering her so much with the roommate agreement that she storms out. Later, Sheldon comes in to see Leonard bringing in a new couch and playing video games, which eventually causes Sheldon to find his spot on the couch. When Leonard comes back to make some rocket fuel for Wolowitz, Sheldon points out that he made a mistake in the fuel formulation. Leonard gets angry, only to realize that it was wrong, and the botched rocket fuel prematurely activates. Leonard thinks he has plenty of time, but Sheldon saved his life by deducing that it is likely to explode while Leonard is attempting to remove it from the building, and resolves the situation by sending it down in the otherwise empty elevator. Leonard explains that the reason he puts up with Sheldon is that he saved his life and did not notify the authorities.

When Penny questions Leonard's responsibility for the experiment that resulted in the destroyed elevator, he asks her what she was doing at the time, and she responds that she was studying, behaving well and doing charity work, when in reality she was jubilantly celebrating with her boyfriend after her pregnancy test showed negative. Afterwards, Leonard returns to the apartment and apologizes for changing the thermostat, which Sheldon accepts only for the two to then immediately get into another argument when Leonard starts watching Babylon 5, which Sheldon hates.

Recurring character: Carol Ann Susi as Mrs. Wolowitz
Guest stars: Ally Maki as Joyce Kim, Steven Yeun as Sebastian, and Ajgie Kirkland as Louie/Louise
Note: This episode reveals that the elevator had been broken for seven years, but in the season one episode, "The Nerdvana Annihilation", Leonard claims that the elevator had been broken for two years, implying that the elevator incident happened in 2006, not 2003.

The guys set up an experiment on the building's roof to bounce a laser off the moon and back to Earth using the laser reflector left by the crew of Apollo 11. On Leonard's request, Penny arrives at the roof with her new boyfriend Zack. During the course of the experiment, Zack turns out to be extremely ignorant and dimwitted, prompting Penny to break up with him, saying that "she could no longer date stupid men." Later that night, Penny enters the guys' apartment drunk and has sex with Leonard. The next morning, Penny realizes what she had done and leaves the apartment embarrassed. Leonard, now thinking it is routine for friends to have "meaningless" casual sex, asks Leslie, and then Penny, to have sex with him, and both slam the door in his face.

Meanwhile, Raj and Howard find a dating website and submit Sheldon's profile to the website without his knowledge. To their surprise, the dating site matched Sheldon with a woman named Amy Farrah Fowler. Sheldon initially refuses to meet Amy as he considers dating sites "hokum", but when Raj and Howard blackmail him by claiming that they hid a dirty sock in the apartment, he agrees to meet Amy. Amy turns out to be the female equivalent of Sheldon- having an aversion to soiled hosiery and physical contact including coitus, sharing Sheldon's disbelief of dating websites and religion and both their mothers' having similar personalities. Sheldon and Amy both hit it off instantly, making Howard and Raj regret what they've done.

Recurring characters: Sara Gilbert as Leslie Winkle, Mayim Bialik as Amy Farrah Fowler, and Brian Thomas Smith as Zack Johnson
Guest star: Lauri Johnson as Mrs. Gunderson
Note: This episode marks the first appearance of future regular cast member Mayim Bialik as Amy Farrah Fowler.