History TheBigBangTheory / SeasonFour

* HeelRealization: Penny realises during The Cohabitation Formulation that Penny is still not over Leonard, given that she breaks down at the thought of him being with someone else because she made a terrible mistake.

* AccidentalInnuendo: 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.''

* ArtisticLicenseChemistry: 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, H[[subscript:2]]S ignites at concentrations between 4.3% and 46%, meaning that the air in Sheldon's office must have contained at least 4.3% H[[subscript:2]]S. 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 probably everyone in the same corridor of Sheldon's office should be dead. And even ignoring its toxicity, high levels of H[[subscript:2]]S can paralyse the olfactory nerve and deaden the sense of smell, rendering Sheldon's plan completely pointless.

* TheBusCameBack: 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.

* TheDogBitesBack: To the point where it nears DisproportionateRetribution in ''The Boyfriend Complexity''. Since Leonard was the only one of Penny's boyfriend 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. [[WhatTheHellHero When Penny goes to chew him out]], Leonard very smugly points out that she should have thought it through.

* SmugSnake: 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 at object.

* TheDogBiteBack: To the point where it nears DisproportionateRetribution in ''The Boyfriend Complexity''. Since Leonard was the only one of Penny's boyfriend 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. [[WhatTheHellHero When Penny goes to chew him out]], Leonard very smugly points out that she should have thought it through.

* EntitledBastard: Penny still expects Leonard to buy her takeout, even though she dumped him. He evens pays for her gas and rent.

* EntitledBastard: Penny still expects Leonard to buy her takeout, even though she dumped him.

* AccidentalInnendo: The night Howard, Bernadette and Raj messing around with a giant space telescope climaxed with Raj accidentally kissing Howard. The following morning...

** ContinuitySnag: 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.

* WhamEpisode: [[spoiler: Raj and Penny waking up in bed together]], which had ramifications that could tear the group apart.

''TheBigBangTheory''

* 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.

* GroinAttack: On "The Zarnecki Incursion, Penny knees the guy who stole Sheldon's ''VideoGame/WorldOfWarcraft'' account.

-->Today's the day a girl is finally going to touch you in your little special place.
* HaveYouTriedRebooting: How the hospital receptionist frees Howard from his robotic hand in "The Robotic Manipulation.

* RomanticFalseLead: 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.