The Big Bang Theory / Season Four

Sheldon begins an odd relationship with his female counterpart, Amy Farrah Fowler. Penny struggles with the realization that it's hard for her to appreciate dumb guys after dating Leonard. Leonard begins dating Raj's sister Priya. Howard and Bernadette get engaged.

Tropes in The Big Bang Theory Season Four

• Animal Hoarding: After Amy breaks up with him, Sheldon starts collecting cats.
  • Series Continuity Error: When Leonard wanted to have a cat in the second season (The Fuzzy Boots Corollary), Sheldon was allergic to them. Leonard found a breeder who had hypo-allergenic ones.
• Artistic License – Chemistry: At one point, Sheldon tries to drive Raj out of his office by filling it with ammonia and hydrogen sulphide. In response, Raj lights an aromatherapy candle, which causes the hydrogen sulphide to explode. Now, H₂S ignites at concentrations between 4.3% and 46%, meaning that the air in Sheldon's office must have contained at least 4.3% H₂S. The problem is, hydrogen sulphide is highly toxic, and concentrations above 0.1% cause instant collapse with loss of breathing. So really, Raj, Leonard and many, many other people should have died. And even ignoring its toxicity, high levels of H₂S can paralyse the olfactory nerve and deaden the sense of smell, rendering Sheldon's plan completely pointless.
  • There was an incident in Real Life where a girl filled a room with roughly 0.1% H₂S, which killed her and sickened 90 other people in her apartment house. The concentration produced by Sheldon was at least 43x higher than this value, so the radius of the area of effect should have been 43x higher. Since the area of a circle is equal to πr², the total area of effect would have been 1849x ^note 43² higher. This means that, assuming the same density of people as in the real-life example, 1849 people should have died, and 166410 people should have been made ill.
  • Then again, this may have just been Rule of Funny
• The Beard: Penny's dad Wyatt came to visit, and had expressed to her how much he preferred her dating Leonard (without having met him) over her prior burn-out boyfriends. To alleviate the nagging she told him that they got back together, and surprised him with a big kiss when they ended up crossing paths in front of Wyatt. She asked Leonard to play along and he was ecstatic, bonding with her dad while giving her sloppy kisses and trying to be an adorable couple.
• The Bus Came Back: Bernadette never actually left; she and Howard just stopped dating. But it is realistic in how people would avoid each other in situations like that.
• "Cavemen vs. Astronauts" Debate: In the ninth episode, the guys debate who the bravest person in the Marvel Universe is.
• Continuity Nod: Leonard asks Howard to honor the girlfriend pact, which was first revealed in season three and how Howard met Bernadette.
• Daydream Surprise: "The Thespian Catalyst" has a series of them involving Raj having sex fantasies about Bernadette.
• The Dog Bites Back: To the point where it nears Disproportionate Retribution in The Boyfriend Complexity. Since Leonard was the only one of Penny's boyfriends that her dad actually liked, Penny lies to him, saying that she and Leonard got back together. Leonard milks the situation for all it's worth, clinging to Penny and slobbering all over her. When Penny goes to chew him out, Leonard very smugly points out that she should have thought it through.
• Entitled Bastard: Penny still expects Leonard to buy her takeout, even though she dumped him. He evens pays for her gas and rent. Taken up to eleven when her dad pays a visit and she expects Leonard to play along with her lie that they got back together.
• Groin Attack: On "The Zarnecki Incursion", Penny knees the guy who stole Sheldon's World of Warcraft account.
  Penny: Today's the day a girl is finally going to touch you in your little special place.
• Have You Tried Rebooting?: How the hospital receptionist frees Howard from his robotic hand in "The Robotic Manipulation".
• Heel Realization: Penny realises during The Cohabitation Formulation that she's still not over Leonard, given that she breaks down at the thought of him being with someone else because she made a terrible mistake.
• High Heel Hurt: In "The Wildebeest Implementation," Amy buys high heels, but feels sore when walking in them.
• Innocent Innuendo: The night Howard, Bernadette and Raj messing around with a giant space telescope climaxed with Raj accidentally kissing Howard. The following morning...
  Leonard: (innocently) You get to play with Raj's big telescope last night?
  Raj and Howard shiver.
• Pet's Homage Name: Sheldon names his cats after the scientists involved in the Manhattan Project. In a case of Odd Name Out, Zazzles is an exception, because he's just so zazzy!
• Prized Possession Giveaway: In "The Apology Insufficiency", Sheldon accidentally ruins Howard's chance at working in a government satellite program by revealing that he once stranded the Mars Rover. Sheldon tries to apologize, but Howard is so angry he rejects it. Out of desperation, Sheldon offers him the thing he prizes most: his spot on the couch! Realizing how serious Sheldon is if he's willing to give up something he values so much, Howard accepts and takes the seat. Sheldon lasts all of ninety seconds before changing his mind and demanding the seat back.
• Romantic False Lead:
  • A classical version in the form of Priya. It really doesn't help that she is highly educated and more of a match for Leonard on an intellectual level.
  • Zach also takes on this role, although played around with extensively in that he was friendly with the guys and Penny admitted she didn't have much feelings for him.
• Smug Snake: Leonard was having a little too much fun maintaining the facade of being a couple with Penny again in The Boyfriend Complexity. Having Penny cringing as he hugged and kissed her and shooting down all her attempts to object.
• Sudden Musical Ending: "The Thespian Catalyst" ends with a Bollywood number by Raj and Bernadette.
• Weirder Than Usual: In one episode, Sheldon and Amy terminate their friendship, and he tries to hide his loneliness by adopting first one cat, then several more. Leonard tries to express his concern to Raj and Howard, who at first don't understand the problem when he says he's worried about Sheldon. Howard notes that they are always worried about Sheldon, whom they described in an earlier episode as being "one lab accident away from a supervillain." After interacting with him and the first cat, Dr. Robert Oppenheimer, they have a better grasp of the situation.
  Howard: Okay, I get it. We're worried about Sheldon.
• Wham Episode: Raj and Penny waking up in bed together in "The Roommate Transmogrification", which had ramifications that could tear the group apart.