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 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."

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.

Leonard and Penny struggle to recover from an awkward 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. 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 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.

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, which does not meet Sheldon's weekly schedule (it's 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. 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.

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 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 trading-card competition 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. Now Sheldon is even more resentful of Wil. 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.

Sheldon, who grew up in Texas where it is popular, teaches Leonard how to understand 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.

Title reference: The football team Penny and her friends watch and the fact that Leonard gets caught up in trying to understand the sport of football to fit in with Penny's friends.

An argument between Leonard and Penny proves "inconvenient" to Sheldon. We learn that Sheldon's parents argued a lot when he was growing up, and he doesn't like to hear people arguing at all. Penny had invited a former lover (male guitarist) to stay at her place without talking to Leonard beforehand, which Leonard was quite upset about, confronting Penny in a way which made her angry. Everyone else was arguing, too: Raj and Howard, Raj and his parents, and Howard and his mother. Sheldon even went to the Cheesecake Factory by himself to try to talk Penny into apologizing to Leonard so he could get on with his life. At the end of the show, Penny's friend is seen sleeping on Sheldon's couch as Leonard and Penny are in bed together in her apartment.

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. Back at home, 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 emergency room. 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 painkillers) is rather happy with Sheldon's help. She gets him to sing Soft Kitty with her.

Wolowitz'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.

Meanwhile, 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 by, 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.

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. Wolowitz gets 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 make love to Wolowitz, 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.

Bernadette's interest in Leonard's work makes Penny jealous that 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.

A visit from Leonard's mother, Dr. Beverly Hofstadter (Christine Baranski) delights Sheldon and horrifies Leonard. Penny is upset because Leonard didn't mention his mother's visit to her, but that is nothing compared to when Leonard learns that Sheldon knows more about his own mother than Leonard does. Leonard learns about his parents' pending divorce, his mother's surgery, and the death of his dog all after Sheldon had known. 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.

Sheldon and Raj attend a university mixer, with Sheldon as Raj's wingman. Sheldon only went because Raj bribed him with a Green Lantern lantern, which Sheldon brought with him to the mixer. 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. Meanwhile, Leonard and Penny go on a double date with Howard and Bernadette, and Leonard is surprised to discover that Penny believes in psychics. He mocks her for it and Penny is furious. 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, while she declines to read a book debunking psychics.

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 American patent office is in 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 (known as Lisa Simpson in The Simpsons). 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. After dropping and breaking a tray of dishes, the scattering of the shattered pieced lead him to the answer to his problem, and he promptly walks out without cleaning up the mess. Meanwhile Raj, Leonard, Penny, Howard, and Bernadette all go to disco night at the roller skating rink. The guys embarrass the women with their outfits and dancing.

Leonard announces that the professor who was invited to a trip to see CERN's Large Hadron Collider in Switzerland was unable to go, so he (Leonard) was designated to be the replacement to go to Switzerland, and he gets to take one guest with him. Sheldon assumes that he would 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. In spite of the agreement, Leonard chooses to invite Penny, as the trip would coincide with Valentine's Day, their first together as a couple. Sheldon tries to pressure both Leonard and Penny to let him go instead, but Leonard insists on bringing Penny and not Sheldon. The night before their scheduled trip, Penny falls ill, so Sheldon is designated to accompany Leonard. However, Sheldon immediately falls ill too, which he suspects he caught when he hugged Penny a day before. Raj therefore accompanies Leonard, and they arrive in Switzerland to a hotel room stocked with champagne, roses, and chocolates.

Sheldon misses his chance to meet comic book legend Stan Lee when he has to attend traffic court after receiving a ticket because of Penny. The ticket was 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 gets put in jail until he is ready to apologize, so he misses Stan Lee at the comic book store signing, where Howard and Leonard get Stan Lee to sign comics books "to my friend." Raj wasn't so lucky, because he was pestering Stan about every character in his comics having the same first and last initials (like Peter Parker and Green Goblin). Later, Penny talks to Stuart and gets 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 (after he was asked to by Lee himself in a sarcastic way, which Sheldon did not understand). 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.

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 remands 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."

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 will help Sheldon psychologically, Penny will shop for a suit with him, and Raj will help with "some kind of Indian meditation crap" according to Howard. When it's time for the speech, Sheldon feels faint, so Penny gives him alcohol, and Sheldon, drunk and behaving like a stereotypical stage comedian, gives a speech that gets put on YouTube under the title "Physicist Melts Down".

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

Title reference: Sheldon takes off his pants during his acceptance speech for the award.

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".

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 has a fight with Sheldon over the setting of the thermostat. He then storms out of the apartment and goes to Penny to cool off. He tells Penny that he should have known about Sheldon based on their first meeting. Leonard then proceeds to tell Penny the story of how he first met Sheldon, making this episode mostly flashback. Leonard starts out by explaining how Sheldon's previous roommate ran out and warned him about Sheldon's idiosyncrasies. Leonard runs into their transvestite neighbor and eventually Sheldon. Sheldon quizzes Leonard on science fiction trivia and allows him to enter after he answers correctly. Sheldon gives a series of interview questions to verify whether or not Leonard is a good and worthy roommate to have. Penny wonders why Leonard continues to live with Sheldon and it is revealed that Sheldon inadvertently kept Leonard from revealing a top secret rocket fuel to a North Korean spy, the previously unseen Joyce Kim (Ally Maki) (who was mentioned in previous episodes) by angering her so much that she storms out and saved his life when he calculated Leonard did not have enough time to travel down the elevator with a batch of incorrectly mixed and unstable rocket fuel. This also destroyed the elevator which forces them to use the stairs. We also learn how Leonard and Sheldon first met Wolowitz and Koothrappali, and how Sheldon came to claim his 'spot' on the new couch.

This episode also includes the first appearances of the previously unseen characters of Joyce Kim, a North Korean spy who dated Leonard for 27 days before defecting back to her country, and the pair's original neighbor, Louie, the "two hundred pound transvestite with a skin condition". Additionally, Sheldon makes a prediction during a flashback that proves to have been wrong, namely that Firefly would run "for years". He also tells Raj that he would be sorry he wasted his money on an iPod when Microsoft "comes out with theirs".

Title reference: After Leonard's unstable rocket fuel explodes and destroys the elevator, the staircase has to be used for transport (and is therefore often featured as a setting for conversations between various characters).

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 dim witted. Later that night, Penny gets drunk and sleeps with Leonard but realizes it was a mistake the next morning. Leonard goes to ask Leslie Winkle to do the same, but gets turned down. After getting drunk, Leonard visits Penny's apartment and asks to sleep with her, which she angrily declines, leaving Leonard 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. Afterwards, Howard comments "Good God, what have we done?"

Title Reference: The guys bouncing a laser off the reflector left on the moon by the crew of Apollo 11 and the excitement about completing the experiment.