Kaley Cuoco's Best Episodes In The Big Bang Theory

Before Kaley Cuoco was solving airport-related murders in "The Flight Attendant" and antagonizing Batman in "Harley Quinn," the actress was well known for playing Penny in the CBS sitcom "The Big Bang Theory." In the series pilot, Cuoco's character is the new neighbor to physicists Leonard Hofstadter (Johnny Galecki) and Sheldon Cooper (Jim Parsons), becoming a fish out of water in their world of science, fandom, and social awkwardness. 

Cuoco played the role throughout the show's run from 2007 to 2019. During that time, her character of Penny formed an on-screen relationship with Leonard, while also building a rapport with Sheldon and characters who joined later like Mayim Bialik's Amy Farrah Fowler or Melissa Rauch's Bernadette Rostenkowski. 

Across the 12 seasons of "The Big Bang Theory," Cuoco often played the straight man in her neighbors' nerdy escapades. The actress has had many shining moments throughout the show, both for herself as an actress and for her character's own journey knowing this colorful cast of geeks. These are some of Kaley Cuoco's most iconic moments playing the role of Penny in "The Big Bang Theory." 

The Pancake Batter Anomaly

Cuoco's early seasons as Penny quickly established many memorable moments for the character, particularly in her relationship with Parsons' breakout character. Penny and Sheldon get a chance to spend some alone time together in the 11th episode of Season 1, "The Pancake Batter Anomaly," in which Sheldon somehow manages to catch a bug, throwing him into a panic. Knowing to keep their distance from Sheldon when he's sick, Leonard, Raj, and Howard escape to a "Planet of the Apes" movie marathon, leaving Penny to take care of Sheldon for the entire episode. It's a great way to introduce the dynamic of these characters, with Penny begrudgingly giving in to Sheldon's various demands, such as rubbing VapoRub on his chest and, most notably, singing a song his mother used to serenade him with when he was sick as a child. 

That song, "Soft Kitty, Warm Kitty," eventually became a recurring joke throughout "The Big Bang Theory," with Penny singing it to Sheldon or Sheldon singing it to others when they need comfort. However, its origin is in this episode, where Cuoco completely nails the performance of Penny slowly realizing why Leonard, Howard, and Raj were so quick to abandon Sheldon when he got sick.

The Tangerine Factor

The will-they-won't-they between Penny and Leonard drives most of the first season, as Leonard's crush on his neighbor steadily grows. It eventually comes to a head in "The Tangerine Factor," which is also the first season finale of "The Big Bang Theory." The episode opens with Penny stewing after a recent breakup, with Leonard debating whether or not he should go over to her apartment to help her.

When a frustrated Penny wonders why she can't ever go out with a nice guy, Leonard finally makes his move and asks Penny to go out with him. Penny's nervousness about the date also results in a hilarious and memorable moment when she asks Sheldon for advice, and Sheldon compares their prospective relationship to the Schrödinger's Cat paradox, which Penny struggles to understand.

Their respective unease eventually climaxes when Leonard shows up at Penny's apartment for their date, and the two kiss for the first time. In one of Cuoco's funniest moments in the show's first season, the kiss ends and Penny, finally understanding the paradox, declares "the cat's alive," before the couple leaves for their first date. 

The Barbarian Sublimation

By the time the second season of "The Big Bang Theory" rolled around, the characters and their dynamics with each other had been established enough where comedy could be earned by turning them on their heads. This was the concept behind "The Barbarian Sublimation," where Sheldon introduces Penny to "Age of Conan," an MMORPG video game.

Very quickly, Penny becomes obsessed with the video game, prompting her to annoy Sheldon with her various questions. It's a fun reversal of Penny and Sheldon's dynamics, given that Sheldon is often intruding on Penny's life by incessantly knocking on her door. After convincing Leonard to try to reason with Penny, Leonard finds the only way he can get through to her is through the video game, though Penny responds to his attempt by chopping his video game character's head off.

The ending of the episode, however, is one of Kaley Cuoco's funniest moments. Dressed in sweatpants and covered in food stains after playing "Age of Conan" for hours on end, she accepts an offer to go out for a drink with Howard's in-game character, which is the only wake-up call she needs to realize that playing this game for so long is unhealthy. 

The Panty Piñata Polarization

While many previous episodes of "The Big Bang Theory" showcase how Sheldon and Penny make unlikely friends, other episodes depict them as mortal enemies destined to take each other down. Their conflict in "The Panty Piñata Polarization" comes to a head when Sheldon bans Penny from their apartment after she eats his onion rings and sits in his favorite spot on the couch. After Penny refuses to take Sheldon's order at The Cheesecake Factory, the two neighbors declare war on each other.

First, Sheldon denies Penny access to their apartment's Wi-Fi, but Penny hits back in a major way: She takes up all the laundry machines on Sheldon's "Laundry Day." Sheldon responds by removing Penny's laundry from the laundry room and leaving it to dry on telephone wires.

The final straw in Penny and Sheldon's war against each other comes when Penny drags Sheldon's mom into the affair. Sheldon receives a call from her insisting he apologize to Penny for how he's been treating her, and he subsequently returns Penny's laundry and revokes his decision to banish her from their apartment. Cuoco proves in this episode that while Penny may not have the scientific intelligence of her neighbors, she's still very much capable of outsmarting them at their own game. 

The Bath Item Gift Hypothesis

Penny and Sheldon have also had their share of endearing moments as friends. In one of the show's most iconic episodes, Season 2's "The Bath Item Gift Hypothesis," Sheldon is put into a stressful situation when Penny announces that she got him a Christmas gift. Sheldon becomes determined to buy her something of equal value, attempting to cover his bases by selecting several bath item gift baskets of varying prices. 

By the end of the episode, even the studio audience is shocked to discover what Penny got for Sheldon. Though he initially seems unimpressed by a napkin from the Cheesecake Factory, Sheldon soon discovers that it's been used and signed by Leonard Nimoy, who visited the restaurant during one of Penny's shifts. Sheldon, ecstatic that he can now grow his own Leonard Nimoy, gifts Penny all of the gift baskets he bought but, fearing that's not enough, Sheldon actually hugs Penny. 

Meanwhile, Penny also spends the episode getting to know David Underhill, a fellow physicist played by Michael Trucco. Leonard is sent into a spiral of his own over this, considering he and Penny broke up due to her insecurity at feeling less smart than him, before the two of them discover that David is actually married, giving Cuoco an opportunity to act Penny's heartbreak alongside her meaningful moment with Sheldon. 

The Work Song Nanocluster

"The Work Song Nanocluster" is another opportunity for Penny and Sheldon to come together with a common goal. At the start of the episode, Sheldon discovers that Penny is starting her own business, selling custom-made flower barrettes she calls "Penny Blossoms." Sheldon decides to start helping Penny streamline her workflow, recruiting the others to help as well. 

To their surprise, they receive an order for 1,000 Penny Blossoms with a tight deadline, thanks to the website Leonard created with the option for "One Day Rush," forcing them all to hunker down and get the Penny Blossoms made within the day. This also leads to a moment where Sheldon drinks coffee for the first time, giving him the idea to don a Flash outfit as he speedily helps them make the Penny Blossoms. 

Though the episode is a simplistic bottle episode only featuring the main five cast members, it's a good showcase of the friend group's willingness to help Penny. Cuoco also once again shines in her interactions opposite Parsons, in what The AV Club called in their positive review of the episode, "another of what's become a string of smartly written, masterfully performed dialogue scenes on this show." 

The Jiminy Conjecture

By the start of season 3, Leonard and Penny's relationship has been restarted, but things aren't going so well for them in the second episode, "The Jiminy Conjecture." After Penny overhears Leonard describing their sex as "just fine," the two have an argument that results in them deciding to get drunk and then have sex to see if that improves. Over the course of the episode, Leonard and Penny get increasingly more and more drunk, while Sheldon, Raj, and Howard have their own separate adventure.

It's a great opportunity to showcase the chemistry between Cuoco and Galecki three seasons in, especially given that the two actors were dating in real life when this episode was filmed and aired. Unfortunately, Leonard and Penny's plan goes awry as the two end up spending the night throwing up in Penny's bathroom rather than having sex as they had planned. 

Thankfully, the two characters are able to mend fences after their night of drinking and puking, ending the episode by deciding to stay friends for a few short seconds before they resume making out. In episodes like this, Cuoco's charismatic on-screen relationship with Galecki might be more intense, but it's certainly still entertaining to watch unfold. 

The Adhesive Duck Deficiency

In a reversal of Season 1's "The Pancake Batter Anomaly," Season 3's "The Adhesive Duck Deficiency" sees Sheldon tasked with the job of taking care of Penny. While Leonard, Raj, and Howard are camping without Sheldon, Penny accidentally slips in the shower and dislocates her shoulder, forcing Sheldon to come over and help her. It's another classic episode where Penny and Sheldon's dynamic is on full display, with perfect performances from Cuoco and Parsons to boot.

Penny's shoulder dislocation results in some high-stakes moments between her and Sheldon, particularly when Penny needs Sheldon to drive her to the emergency room, even though Sheldon cannot drive. In reaction to Sheldon's slowness, Penny quips at one point, "Warp speed ahead, Mr. Spock," which showcases that despite having no interest in the group's nerdiness, Penny has learned more than she's willing to admit about "Star Trek."

The real kicker at the end of the episode is, after their emergency room visit, Sheldon takes Penny back to her apartment, where she requests that Sheldon sing "Soft Kitty, Warm Kitty" to comfort her. It's the first time in the show that Sheldon sings the song instead of Penny, but it makes for one of the sweetest moments between these two often adversarial characters.

The Gorilla Experiment

In most of the early seasons of "The Big Bang Theory," Leonard was the one trying to impress Penny. However, Season 3 sees an interesting reversal of that with its 10th episode, "The Gorilla Experiment," which opens with Penny impressing Sheldon by explaining to Bernadette why Sheldon chooses to sit in his special spot on the couch. Penny later takes Sheldon up on his offer to teach her more about physics in an attempt to impress Leonard.

Predictably, Sheldon's lessons for Penny are more complicated than they need to be, starting in Ancient Greece and guiding Penny through the most important events in scientific history. In an iconic moment between the two, Penny cries over her inability to understand these concepts, prompting Sheldon to comfort her by telling her that being stupid is no reason to cry, though he does sometimes cry over other people's stupidity. 

Though Penny does eventually get a moment at the end of the episode where she showcases her knowledge of science to the group, they eventually realize she's just parroting things that Sheldon has taught her. Thankfully, Penny doesn't have to worry too much about impressing Leonard in future episodes, as by Season 6 she's able to accomplish that by donning a pair of glasses and simply saying "Molecules" to him.

The Rothman Disintegration

It wasn't long before Kaley Cuoco wasn't the only female main cast member on "The Big Bang Theory." Soon enough, Melissa Rauch and Mayim Bialik joined as Bernadette and Amy, becoming romantically intertwined with Howard and Sheldon, respectively. The three women's relationship with each other takes center stage in Season 5's "The Rothman Disintegration." 

Amy, over-enthusiastic about being friends with Penny, shows up at her apartment with a gift: A massive, awkward painting of the two of them. She brings Bernadette over, who confirms Penny's fears that the painting is ugly, though Penny hesitates to throw it out, fearing that she'll hurt Amy's feelings. Penny begins taking the painting down when Amy's not there, though when Amy catches her in the act, their friendship is put into turmoil.

After Penny makes up for it by bringing the painting back to Amy's, the two remain friends. Overall, the episode is a great display of not only Penny's friendship with both Amy and Bernadette, but also Cuoco's own chemistry with Rauch and Bialik, which will continue to shine through the remaining seasons of "The Big Bang Theory." However, few moments shine better than Cuoco's performance of Penny learning that the original painting Amy got for her had them in the nude. 

The 43 Peculiarity

"The 43 Peculiarity" is the eighth episode of Season 6 of "The Big Bang Theory," and also happens to hold a special place in the heart of Kaley Cuoco, as well as Leonard and Penny shippers. The episode mostly centers on Penny's time taking college classes, where she strikes up a friendship with her class partner, Cole, whom Leonard quickly becomes jealous of. Penny becomes increasingly frustrated when Leonard tells Cole to back off.

Later on, the two run into each other in the hallway, where Penny confronts Leonard over his jealousy and insecurity about their relationship. Unintentionally, Penny reminds Leonard that she loves him, which stuns him as it's the first time that Penny's ever said that to him. The conversation quickly ends after that to avoid both of them crying in front of each other. 

Cuoco later singled out this episode as one of her favorites, particularly for the final scene between Leonard and Penny, which is a huge moment in their relationship. As Cuoco described about filming the scene, "That was one take and done!!" (via TBS). It makes sense that six seasons in, scenes like that were likely incredibly easy to film for a cast who were so close and comfortable with each other.

The Occupation Recalibration

By the time Season 7 rolled around in "The Big Bang Theory," things were quite fraught in Leonard and Penny's relationship. In the episode prior, Penny had drunkenly proposed to Leonard after feeling sad about her role in a television show being cut. However, in this episode, "The Occupation Recalibration," Penny makes another brash choice that Leonard struggles to react positively to: She quits her job at the Cheesecake Factory.

Penny ends up spending the rest of her day with Sheldon, who is being forced to take a vacation from his job, while debating whether or not she should be worried about having quit her job. After Sheldon supports Penny's decision, the two end up doing yoga together, even though Sheldon claims that he was convinced to do it because he thought that Penny had said "Yoda." 

Although Penny and Leonard eventually make up with each other by the end of the episode, it's a cute moment where Sheldon and Penny's friendship over seven seasons has blossomed to a place where he's supportive of her decisions, as risky as they may be. 

The Celebration Experimentation

"The Celebration Experimentation" marked an important moment for "The Big Bang Theory," as it was the 200th episode of the show. Airing as the 17th episode of Season 9, most of the story takes place during Sheldon's 36th birthday party, which causes a lot of feelings to rise up as a result of his poor childhood experience with birthdays after sharing them with his twin sister, Missy. However, Amy insists they throw a party for him.

Despite Sheldon's various demands, Amy, Penny, and Bernadette do a great job organizing it, even inviting Adam West as a guest appearance. However, Sheldon panics upon entering and hides in the bathroom, resulting in the characters debating how to get him out. This is where the episode becomes an incredible showcase of Kaley Cuoco's evolution of Penny over nine seasons.

After entering the bathroom to comfort Sheldon, Penny endearingly tells him that everyone showed up because they love him, and that she'd be willing to spend his birthday party in the bathroom with him. This episode, especially this moment, shows what Cuoco was best at while playing Penny for 12 seasons: She may not have the brains or the nerdiness of the rest of the characters, but she has the heart and emotional intelligence they all need in their lives.