List of The Big Bang Theory episodes (season 3)

After their return home from their three-month expedition in the North Pole, Sheldon finds out from Howard and Raj that the guys had tampered with his magnetic monopole experiment because Sheldon was absolutely unbearable when he wasn't getting the results he wanted (plans to kill him were even brought up and discussed). They tell him about their use of an electric can opener to give Sheldon positive results, thereby causing Sheldon to believe he has made a Nobel Prize-winning discovery. Unfortunately, Sheldon had immediately emailed everyone at Caltech about his discovery before Howard and Raj could tell him what had happened. Sheldon is so disgraced that he resigns and moves back in with his mother (played by Laurie Metcalf), who lives in east Texas. Mrs. Cooper calls Leonard and tells them that they should come talk to Sheldon. Upon the guys' arrival, Sheldon is intent on staying in Texas. However, he shortly has a disagreement with his mother about creationism versus evolution and decides to return to California.

Meanwhile, Penny has been harboring feelings for Leonard, which are released almost as soon as he comes home. Leonard's "moments" with her are constantly interrupted, and he "cannot catch a break." They finally sleep together at the end of the episode (Leonard finally "catches his break") and Leonard asks why it's always weird after friends sleep together and why they have to label it as such - "it just is what it is." Penny interrupts him saying "it's weird" and he replies "Totally."

Recurring characters: Laurie Metcalf as Mrs. Cooper, John Ross Bowie as Barry Kripke

References: When Raj names Howard's moustache he calls it the Mario & Luigi. This is a reference to Mario's and Luigi's moustaches from the Mario series.

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 hears the chirps and says it is a snowy tree cricket and Howard insists it is a common field cricket. Along with Raj, the three spend a while locating the cricket. They settle the bet by taking "Toby" to Caltech's depressed entomologist, played by Lewis Black. Howard is correct that it is a common field cricket, so Sheldon has to give up his copy of The Flash.

Meanwhile, Leonard and Penny struggle to recover from an not-so-great first hookup and try to figure how to overcome their current problem. A romantic evening between the pair soon turns to 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 don't work out, they can always return back to being friends. After Sheldon tells Leonard that he spoke to Penny about their problems, Leonard goes to Penny's apartment, there 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's clear that neither wants that and soon give in to their attraction.

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, missing their opportunity with the girls rather than having tattoos.

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. Penny then makes French toast for breakfast and offers some to Sheldon, which he does not accept (it's Monday, which according to his weekly schedule is oatmeal day). During the episode, Sheldon tries to improve Penny using chocolate, rewarding her for what he considers to be correct behavior, as in operant conditioning with lab rats, despite Leonard's opposition.

References 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 series are co-created by Chuck Lorre. This is also the first time in the third season in which Sheldon brings back his "catchphrase" "Bazinga".

Raj must find a new job or be sent back to India. Sheldon has a solution, which is to allow Raj to work "for" him, rather than work "with" him. Raj reluctantly accepts the offer. With Raj working for Sheldon, it makes Howard lonely, so he tries to stay with Leonard and Penny (even making them breakfast) but they would rather be alone. Sheldon and Raj soon 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 doesn't concede to him being wrong.

Sheldon enters a collectible card game tournament when he hears Wil Wheaton, for whom he harbors resentment for not attending a Sci-Fi convention, is also participating. With Raj as his partner, they reach the final match against Stuart and Wil Wheaton. Sheldon could have won, but Wil told him how he did not attend the convention due to his grandmother dying, which was a ploy to get Sheldon to let Wil win, leaving Sheldon even more resentful of him

Meanwhile, 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. She does and they go on a double-date, but Howard and Bernadette (Melissa Rauch) don't have anything in common until they learn about each other's problems with their mothers.

Recurring characters: Wil Wheaton as himself, Kevin Sussman as Stuart and Melissa Rauch as Bernadette Rostenkowski

Sheldon, who grew up in Texas where it is popular, teaches Leonard how to understand American football so that he can try to fit in with Penny's friends. During the game Leonard attempts to demonstrate what he has learned, but his explanations are too clinical, and he fails to fit in.

Meanwhile, Raj loses his kite to Sheldon in a kite fighting contest because Howard abandons him at a critical moment to chase a girl. Howard makes it up to him by spending a Saturday afternoon with Raj at the La Brea Tar Pits, only to chase after another girl.

Note: This episode featured Sheldon making "cylon toast", using a Battlestar Galactica themed toaster.

When Penny invites a friend and former lover of her, who is a "definitely not gay" guitarist, to sleep on her couch, Leonard becomes upset. They start a fierce argument, which Sheldon tries to resolve because of certain childhood memories he has about his parents arguing. He talks to Penny and Leonard to get them to apologize, but none of them is willing to admit that they were wrong. As a result, Sheldon runs away. He tries to find shelter at Raj's apartment and Howard's house, but as they are both arguing with their parents, he ends up in the comic book store. In the end, Leonard and Penny get Sheldon to come home again by buying him a robot and a comic book. Penny's friend is then seen sleeping on the couch in Leonard's and Sheldon's apartment, prompting Sheldon to say "I should have asked for much more than a comic book and a robot."

Recurring characters: Kevin Sussman as Stuart

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 an emergency department. Penny is neither dressed (yet) nor can she drive her car. Sheldon 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.

Leonard is with Raj and Howard on a camping trip to watch the Leonid meteor shower, but all three succumb to 'magic' cookies they get from Deadhead campers nearby. Hilarity ensues as their minds expand and the munchies set in.

Barry 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 announcing defeat, Leonard and Raj (originally enjoying the prank), convince Sheldon to fight back. Sheldon takes vengeance on Kripke with an elaborate trap in which a massive cloud of gooey foam, to be set off by a human presence in Kripke's office, falls through the ceiling into Kripke's office, effectively covering him in foam. However, the trick backfires on him when the visiting Caltech president and board of directors are also hit, thanks to Sheldon's lack of an "abort" system. Sheldon gives himself away with a pre-recorded video stating that he 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.

Meanwhile, Howard's new girlfriend, Bernadette, asks him where their relationship is going after their third date. He avoids her for a week, thinking about whether he should "settle" for her or hold out for the impossible (Megan Fox from Transformers being interested in him). 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, gets rejected, and then sings her his version of the song "Bernadette" (by the Four Tops) in order to win back her affections, in which he becomes successful when she declares it as the most romantic thing anyone has ever done for her.

Recurring characters: Melissa Rauch as Bernadette Rostenkowski and John Ross Bowie as Barry Kripke

Bernadette, in the guys' apartment for dinner, shows an interest in physics, particularly in the work that Leonard is conducting. Leonard offers her the chance to come tour his lab and watch him conduct an experiment. Penny gets jealous because she doesn't have enough background in physics to talk to Leonard about his job. She therefore seeks out Sheldon to teach her physics so that she would be able to relate to Leonard and discuss his work. In spite of his initial refusal, he agrees to take on the challenge of teaching physics to Penny. At the end of the show, while having dinner in the apartment, Penny spouts off a clearly prepared spiel which Sheldon has coached her in, repeating Sheldon's viewpoint that Leonard's experiment is functionally identical to the one conducted by a Dutch team of scientists.

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

Recurring characters: Melissa Rauch as Bernadette Rostenkowski

It's Christmas and Leonard's mother, Dr. Beverly Hofstadter (Christine Baranski) visites a horrified Leonard and a delighted Sheldon. Penny is upset because Leonard didn't tell her about his mother's visit nor his mother about their relationship. This problem gets 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 after 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 when they get back to the apartment, a somewhat inebriated Beverly gives Sheldon a deep, long kiss, but by the end of the episode they agree to keep that a secret from Leonard.

Recurring characters: Christine Baranski as Dr. Beverly Hofstadter

Leonard and Penny's relationship hits an impasse when, while on a double-date with Howard and Bernadette, she reveals that she takes career advice from a psychic, only for Leonard to laugh at her, infuriating her. Later, Howard shows Leonard that if he wants to be able to ever be in a relationship, he'll 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 brings with him to the mixer, in case evil strikes. They meet Abby (Danica McKellar), who takes a liking to Raj, and her friend Martha (Jen Drohan), 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 come into his room to avoid Raj and Abby, who are "getting busy". Sheldon obliges but immediately leaves to sleep in Leonard's room instead, leaving Martha alone.

Recurring characters: Melissa Rauch as Bernadette Rostenkowski

When their apartment is robbed and their TV, video games, and computers are stolen, Leonard and Sheldon turn to Howard to create a state-of-the-art security system, which includes an electrified net over the door. Sheldon gets caught in that net and decides he needs to leave Pasadena. He gets online and rules out several cities for different reasons, including Enid, Oklahoma, and Boone, North Carolina. He rules out all of Nebraska because Penny is from there. He decides on Bozeman, Montana, but gets robbed as soon as he arrives there, so he comes back to Pasadena. It is revealed that Sheldon considers Howard as an acquaintance and the others as close friends.

Sheldon's search for the answer to a physics problem keeps him up all night for several days and he becomes obsessed with finding the answer. One attempt in a mall ball pit has Leonard jump in and try to get Sheldon out as he pops in and out, shouting "Bazinga!". He then decides that he needs a menial job to think better because Albert Einstein came up with the Theory of Relativity while working a menial job at the Swiss patent office. Since the United States Patent and Trademark Office is near Washington DC, and he doesn't want to move out of Pasadena, he interviews for any menial job with the County of Los Angeles, where he is interviewed by a woman played by Yeardley Smith. Since he is tossed out, the next menial job he can think of is to work at the Cheesecake Factory with Penny. He shows up and works as a busboy and waiter, but never is actually hired, although as he does not want pay, the restaurant appears happy to let him continue, and he turns out to be a much more efficient waiter than Penny. After dropping and breaking 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. The men embarrass the women with their outfits and dancing.

Recurring characters: Melissa Rauch as Bernadette Rostenkowski

Leonard announces that the professor who was to attend a conference in Switzerland and visit CERN's Large Hadron Collider is unable to go, so he (Leonard) has been designated to be the replacement, and he gets to take one guest with him. Sheldon is pleased, assuming that he will be Leonard's guest because they have a roommating agreement that if one roommate gets invited to see the Collider, he would invite the other (Sheldon having always wanted to see it). In spite of the agreement (which Leonard had thought was frivolous), Leonard chooses to invite Penny, as the trip would coincide with Valentine's Day, their first together as a couple. Sheldon is upset and tries to pressure both Leonard and Penny to let him go instead, but Leonard insists on bringing Penny and not Sheldon, and Sheldon eventually decides to terminate their friendship. The night before their scheduled trip, Penny falls ill, so Leonard decides to ask Sheldon to accompany him. However, he discovers that Sheldon has also fallen ill, which he suspects he caught when he hugged Penny a day before. As a result, Penny spends Valentine's Day with Sheldon. Leonard, knowing Raj had nothing to do for Valentine's Day, decides to take him to Switzerland instead. They arrive to a hotel room stocked with champagne, roses and chocolates, something that disappoints Leonard as he had forgotten he had ordered it, but which greatly excites Raj, who declares this to be the best Valentine's Day ever.

Sheldon misses his chance to meet comic book legend Stan Lee when he has to attend traffic court after receiving a traffic ticket because of Penny. The ticket originates from a traffic camera catching Sheldon running a red light in Penny's car when he was taking her to the hospital in The Adhesive Duck Deficiency. After insulting the judge, Sheldon is put in jail until he is ready to apologize, thus missing Stan Lee at the comic book store signing, where Howard and Leonard and Raj get to meet Stan Lee for signing their comic books. Afterwards, they all eat gelato with him. It is implied multiple times that Raj pissed Stan Lee off, because he was pestering him about every character in his comics having the same first and last initials (e.g. Peter Parker or Green Goblin). Later, Penny talks to Stuart to get Mr. Lee's address, and she and Sheldon show up there unannounced. Stan Lee then applies for a restraining order against Sheldon for entering his house. When Sheldon announces his "autographed" restraining order to the guys he comments it will look great hanging next to his restraining order from Leonard Nimoy.

Trivia: The judge's name is J. Kirby, a comic collaborator with Stan Lee.

Recurring characters: Kevin Sussman as Stuart

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."

Note: This was the most watched episode of season 3 and is the most watched episode of the whole series so far, with more than 16.31 million viewers.

Sheldon's friends come to his aid when his fear of public speaking stands between him and a coveted award. They offer to be Sheldon's X-Men, which Sheldon changes to his "C-Men" because his last name is Cooper. Leonard helps Sheldon psychologically, while Penny, in an attempt to boost his confidence, takes him to shop for a new suit. According to Howard, Raj shows Sheldon "some kind of Indian meditation crap", while he himself helps by pretending to "give a damn". Sheldon's "C-Men" all fail more or less and Leonard has an emotional breakdown, as his mother never acknowledged anything he had achieved. When the evening for the speech finally arrives, Sheldon panics and feels faint. Penny suggests that drinking alcohol might help, but as Sheldon has no experience with drinking whatsoever, he gets hammered and acts like a stereotypical stage comedian. His "speech", during which he removes his pants, gets put on YouTube under the title "Physicist Melts Down".

Trivia: The song Sheldon sings at the ceremony is the song "The Elements" by Tom Lehrer.

Note: Jim Parsons won a Primetime Emmy Award for Outstanding Lead Actor in a Comedy Series for this episode.

One night after having sex, Leonard surprises Penny by saying "I love you" but she can only say "thank-you" and they both start to think about where their relationship is heading. The next day, Penny and the guys are in a bowling match with Stuart and the gang from the comic book store. Since one of the comic store's team members couldn't come they got Wil Wheaton to substitute. Sheldon vows to get revenge for what happened in The Creepy Candy Coating Corollary. During the match, Penny and Leonard are eating, at which point Penny says that she loves chili cheese fries. Since she used the word "love" to describe her feelings for the chili cheese fries, this gets Leonard upset, as she could not use that word to describe her feelings for him. They have a fight, and Penny walks out. This causes the gang to forfeit the bowling game. Sheldon, very distraught that they had to forfeit, gets Leonard and Penny to talk and supposedly patch things up. They go back to the alley where Sheldon and Wil both try to beat each other in the game. Wil talks to Penny and tells her that he endured two years of misery with a girlfriend who could not say "I love you" to him. Sheldon's team, the "Wesley Crushers" (in reference to Wheaton's character on Star Trek: The Next Generation) needs one strike to win or they lose a bet. It's Penny's turn to bowl, but leaves again after Leonard pressures her as she worries that she will never be able to say "I love you" to him. Leonard realizes it may all be over between him and Penny. After losing the game, Sheldon confronts Wheaton for what he said to Penny, and Wheaton reveals that he intentionally broke up Leonard and Penny so that they would forfeit the match. The episode folds with the four guys walking into the comic book store dressed like Catwoman (Raj), Batgirl (Howard), Wonder Woman (Sheldon), and Supergirl (Leonard), since they lost the bet to Wheaton and Stuart. Koothrappali remarks that the outfit makes him feel "empowered".

Recurring characters: Wil Wheaton as himself and Kevin Sussman as Stuart

Leonard and Penny have broken up. Sheldon meets Penny in the hall and invites himself to visit her in an hour for spaghetti with hot dogs. Faced with Howard's explanation that, after a break-up, friends of the couple must pick sides, Sheldon hides his dinner plans from the guys and eats with them first. He then wants to go across the hall to Penny's apartment, but because Wolowitz is leaving at the same time, he cannot go directly to Penny's place and instead has to leave the building with Wolowitz. Outside the building, Sheldon runs into a vicious hound who can smell the hot dogs that Sheldon hid under his shirt for the purpose of taking to Penny. The dog gives chase so Sheldon has to throw away most of the hot dogs. When Sheldon reaches Penny's apartment all out of breath and with only one hot dog, they have dinner (Penny cut up the hot dog and put it in the spaghetti) and Sheldon confesses his continuing friendship with Penny to Leonard, who says he doesn't mind. The remainder of the episode plays as if Leonard and Penny are a divorced couple with joint custody of a child, Sheldon. Penny takes Sheldon, who is terrified of Goofy, (whom Sheldon has a nightmare about at the end of the episode) to Disneyland. At the end of the episode, Penny pronounces that she and Leonard can stay friends. Leonard tries to push it by asking for a relationship of friends with benefits but Penny flatly rejects this proposal.

Dr. Elizabeth Plimpton (Judy Greer), a cosmological physicist from Princeton University, comes to Cal Tech for a job interview. 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 three guys, but Raj manages to lock the other two out of the apartment. 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]".

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 first flashback begins 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 periodic table 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 Howard and Raj, and the acquisition of the couch 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 (Ally Maki), a North Korean spy, by angering her so much that she storms out. Later, when Leonard's botched miniature rocket and prematurely activated, Sheldon saved his life by deducing that was likely to explode while Leonard attempted to remove it from the building, and by sending it down in the otherwise empty elevator. (This incident also explains the permanently out-of-order elevator, and their invariable use of the stairs.)

First-time characters: Joyce Kim, North Korean spy; Louie/Louise, former neighbor.

The guys set up an experiment on the building's roof to bounce a laser off the moon and back to Earth. Leonard thinks Penny might enjoy that, so he goes to get her, only to find she has male company. Penny and her date accompany them to the roof to observe the experiment. However, in the course of doing so, Penny's date demonstrates himself to be extraordinarily dimwitted. Later that night, Penny gets drunk and sleeps with Leonard but realizes it was a mistake the next morning. Twice, Leonard attempts to convince someone (Penny and Leslie Winkle) to sleep with him, but ends up getting turned down, leaving him confused.

Meanwhile, Howard and Raj submit an online dating site profile for Sheldon that surprisingly results a match. Sheldon believes dating sites to be "hokum," and refuses to meet the woman the site found for him. After Raj and Howard blackmail Sheldon by hiding a dirty sock (an acute fear of his) in his apartment, they meet his match, Amy Farrah Fowler (Mayim Bialik). She acts almost exactly like Sheldon, who asks to buy her a drink after they agree to "no touching" and "no coitus" parameters to their "date". Afterwards, Howard comments "Good God, what have we done?"

Recurring characters: Sara Gilbert as Leslie Winkle, Mayim Bialik as Dr. Amy Farrah Fowler, and Brian Thomas Smith as Zack Johnson.

Guest Star Note: Penny's date from this episode is Brian Thomas Smith from CBS' The Amazing Race (Season 7).