For over a decade, “The Big Bang Theory” was one of the most-watched shows on television. The sitcom follows the lives of scientists Leonard Hofstadter (Johnny Galecki), Sheldon Cooper (Jim Parsons), Howard Wolowitz (Simon Helberg), and Raj Koothrappali (Kunal Nayyar) as their friend group is upended by Leonard and Sheldon’s new neighbor Penny (Kaley Cuoco), whom Leonard falls for. As the series goes on, Sheldon and Howard welcome their own love interests in Amy Farrah-Fowler (Mayim Bialik) and Bernadette Rostenkowski (Melissa Rauch). 

Even as the multi-cam sitcom format has waned in recent years, “The Big Bang Theory” maintained a strong audience across all demographics throughout its entire run, and was followed by the successful spin-off “Young Sheldon,” as well as another brand-new spin-off, “Georgie & Mandy’s First Marriage,” which premiered in 2024. Even five years after ending, “The Big Bang Theory” remains one of the strongest television franchises of all time. 

However, despite its mass appeal, there are a lot of questionable things we ignore in “The Big Bang Theory,” from subtle sexual innuendoes to behind-the-scenes facts that go over the heads of many viewers, These aspects of “The Big Bang Theory” may seem obvious to some of the adults in front of the TV screen, but for a lot of fans, they can go completely unnoticed. 

Considering “The Big Bang Theory” primarily centers on a friend group of scientists, there are plenty of details that will unlock your inner nerd, especially when it comes to real scientific theories. One notable example of this is in the first season episode “The Tangerine Factor,” when Sheldon explains “Schrödinger’s Cat” to Penny in an effort to calm her nerves over her impending first date with Leonard. After Penny and Leonard kiss at the end of the episode, Penny makes a callback to the theory by saying, “Alright, the cat’s alive, let’s go to dinner.” 

The show’s exploration of complex scientific principles isn’t just made-up, either, as CBS employed science advisor David Saltzberg to fact-check scripts, and even provide insight into math equations and props featured on-screen. In an interview with Symmetry, Saltzberg described his contributions as uncomplicated, saying, “[The writers] explained to me in the beginning that you can watch an ‘I Love Lucy’ rerun and not understand Spanish, but understand that Ricky Ricardo is angry. That’s all the level of science understanding needed for the show.”

Among some of the other scientific theories the show has referenced are the Born-Oppenheimer approximation and the Doppler effect, though there have also been moments when the writers got science wrong, such as the super asymmetry theory that wins Sheldon a Nobel Prize in the series finale. 

“The Big Bang Theory” featured a whole slew of guest stars over its 12 seasons, from the likes of LeVar Burton to Stephen Hawking. The ones that resonated the most are the ones who the characters, as well as older viewers, are most nostalgic for. One example is the Season 7 episode “The Convention Conundrum,” in which Sheldon serendipitously spends a day with James Earl Jones, the iconic voice of Mufasa and Darth Vader, which culminates in them ding-dong-ditching Princess Leia herself, Carrie Fisher (who, funnily enough, Jones had never met in person before this episode). 

Some of the celebrity cameos in “The Big Bang Theory” even include figures who are not as beloved now as they were when the episode aired. Elon Musk offered one of the show’s most cringeworthy moments in his interaction with Howard at a soup kitchen in Season 9’s “The Platonic Permutation,” though younger viewers probably don’t know how significant that appearance is now.

Nevertheless, many exalted icons of nerd-dom made appearances on the show, like Stan Lee in the third season, or Katee Sackhoff in Seasons 3 and 4. The show even roped in historical figures of science for cameos, like Apple co-founder Steve Wozniak and astronaut Buzz Aldrin. 

The portrayal of neurodiversity on television has been an issue long before “The Big Bang Theory” premiered. The character of Sheldon in particular has been analyzed through the lens of autistic behavior, with some critics noting that the show fell short in its characterization of the latter despite star Jim Parsons’ earnest attempts at a realistic, empathetic portrayal.

Among the many examples critics point to as evidence of Sheldon’s neurodivergence is his particular obsession with a specific spot on the couch in his shared apartment with Leonard. As Sheldon explains in the very first episode, “Pilot,” he prefers the seat due to its location in the living room relative to the temperature of the room, as well as its positioning toward the TV. While there are aspects of the behavior that are clearly neurodivergent, many critics have seen it, as well as shows like “The Good Doctor,” as offering a narrow-minded perspective of neurodiversity. 

Creator Chuck Lorre avoided labeling Sheldon for a good reason, believing it too much of a responsibility to represent neurodiversity by diagnosing Sheldon. However, the other characters on the show each contain harmful traits of autism, from Raj’s selective mutism to Amy’s social awkwardness. Younger viewers, however, may clock all these serious behaviors as simply “quirky.”

There are plenty of adult jokes that younger viewers are likely to miss in “The Big Bang Theory,” but in all fairness, so is Sheldon Cooper. One of the character’s defining traits throughout the series has been his naïveté when it comes to sexuality, whether it’s his unawareness of other people’s social boundaries, or just plain old ignorance toward how women or sex work. In the Season 6 episode “The Closet Reconfiguration,” Sheldon is cleaning Penny’s closet when he asks if she had a dog (after finding a “battery-operated chew toy”), to which Penny abruptly pushes Sheldon out of the apartment, implying that what Sheldon actually found was a vibrator.

Other episodes showcase near-comical levels of incompetence from the supposedly-genius Sheldon. In Season 3’s “The Adhesive Duck Deficiency,” Sheldon helps an injured Penny get dressed, only to grab something else instead of her broken arm. The character’s disinterest in sexuality has led many to speculate that Sheldon is asexual, a label “The Big Bang Theory” was committed to until it wasn’t. Even Chuck Lorre defended the character’s behavior early on, remarking (via Entertainment Weekly), “We’ve stumbled into creating a character who has chosen a lifestyle for himself that is unique. And I don’t see any reason to modify it.” Inevitably, they did modify Sheldon’s asexuality by introducing Amy into the show, with the two finally consummating their relationship in Season 9. 

Fun fact: Throughout all 12 seasons of “The Big Bang Theory,” Leonard’s glasses never have lenses in them. The same is even true for all the characters who wear glasses, including Amy and Leslie. Though this detail may distract viewers every time they watch “The Big Bang Theory,” there’s a very specific reason for the absence of lenses. 

The real reason Leonard’s glasses didn’t have lenses in “The Big Bang Theory” predates the very first episode, when Johnny Galecki decided he wanted Leonard to wear glasses during rehearsals. However, donning them posed a problem for the production due to Galecki’s height difference with Jim Parsons, with the lenses catching a glare from lighting rigs whenever he’d look up at his frequent co-star. 

Despite this very specific attention to detail, there have been lots of other mistakes in “The Big Bang Theory” that older viewers could notice if they watch closely enough. Whether it’s a continuity error regarding a character’s history, or the strange way every character uses a salt and pepper grinder as if it’s a shaker, the fact that many viewers could watch the entirety of “The Big Bang Theory” and never notice Leonard’s empty eyeglass frames is remarkable. 

The Penny that Leonard and Sheldon meet in the first episode of “The Big Bang Theory” is very different from the one Kaley Cuoco transforms into by the show’s end. Initially, Penny’s move to California is spurred by her desire to become an actress,  an on-and-off passion of hers throughout the series that she ultimately abandons in Season 8 to work for Bernadette’s pharmaceutical company. 

While it lasted, however, Penny’s acting career featured some head-scratching roles that only adult viewers would understand. Among the more notable was “Serial Ape-ist,” a B-movie centered on a sex-crazed killer gorilla, in which Penny infamously appeared topless. Obviously, the title of the film is a crude-enough joke from the writers, but a vanity card from co-creator Chuck Lorre at the end of Season 7’s “The Indecision Amalgamation” alludes to the film’s sequel being written by “Breaking Bad” creator Vince Gilligan. 

The other roles Penny takes on throughout “The Big Bang Theory” also include some pretty significant instances of adult humor. She mentions a bowling alley production of “The Diary of Anne Frank” several times, and at the start of Season 5, she books a role in a hemorrhoid cream commercial that convinces her not to move back home to Nebraska.

Although the cast of “The Big Bang Theory” are quite a lovable group of characters, Howard stands out in earlier seasons as the most divisive. From the very first episode, Howard is portrayed as a big sleazeball who goes to desperate lengths to pick up women, no matter how pathetic it makes him look. 

The caveat to this distinctly unlovable quality is Howard’s tendency to fail when trying to court women who are way out of his league. Adult viewers, especially women, probably relate heavily to the concept of a dorky guy trying way too hard to win their affection, even when the social cues are not in his favor. Things change after Howard meets Bernadette, but it doesn’t change the fact that one of the the creepiest things Howard ever did on “The Big Bang Theory” was spying on Penny via a hidden camera in her apartment.

Many felt the introduction of Melissa Rauch as the perfect foil to Howard’s character saved him from remaining a flawed character throughout the entire show. However, the counter-argument is that even though Howard no longer flagrantly chases women once he’s in a committed relationship, he still exhibits sexist tendencies by expecting his partner to take care of his needs without him reciprocating or taking on any duties in the household.

“The Big Bang Theory” is certainly not the first sitcom to dabble in homophobic jokes, but when it does, it always seems to raise questions about the character of Raj that only more mature audiences would really understand. Raj’s dialogue has a tendency to tread into innuendo territory, such as one scene in Season 4’s “The Bus Pants Utilization,” when he naively tells Howard about a dream he had where they become rich and live in side-by-side mansions.

As Raj reveals, “There was a secret tunnel connecting your front yard to my backyard. What do you think that means?” Judging by Howard’s expression (and the audience’s roaring laughter), he knows all too well what that suggests about Raj’s inner psyche. And this isn’t the only instance where Raj’s dreams allude to the idea that he might be something other than straight. In another Season 4 episode, Raj fantasizes about falling in love with Bernadette in a flashy Bollywood-esque dance sequence; when he emerges from the fantasy, he outwardly states, “Dance number aside, I’m so not gay.” 

A lot of critics felt that “The Big Bang Theory” failed to ever explore the layers underneath Raj’s character, whether it pertained to his sexuality, his chances at finding love, or any kind of emotional growth. If only he was the character popular enough to get his own spin-off instead of Sheldon. 

Mayim Bialik’s Amy Farrah-Fowler was a welcome addition to the main cast of “The Big Bang Theory,” though it didn’t stop some viewers from pointing out her very peculiar behavior around Penny. Some fans have speculated that Amy has unreciprocated feelings for Penny, which is evidenced by one particular episode in the show’s fifth season, “The Rothman Disintegration.” In the episode, Amy gifts Penny a large painting of the two of them that she commissioned for $3,000, which Penny reluctantly keeps despite being very weirded out by it. 

One notable quote from Amy in the episode is when she tells Penny that the artist behind the painting had originally drawn them nude, before adding clothes after Amy “thought it was an unnecessary challenge to our heterosexuality.” In one of the show’s darkest jokes, a later episode sees Amy drop the bombshell that the artist behind the painting committed suicide shortly after completing it, which only adds to its creepy aura.

Aside from raising questions about Amy’s relationship with Penny, the painting is also responsible for some noteworthy continuity errors in Season 10. After Amy and Sheldon move into Penny’s old apartment, they return the painting to Penny across the hall after she “accidentally” leaves it behind. However, later in the season, the painting has mysteriously returned to Penny’s old apartment. Perhaps the only thing creepier than Amy’s affection for Penny is this painting that moves all on its own. 

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“The Big Bang Theory” often incorporates dark humor, especially when it involves Howard, but rarely is a line of dialogue so profoundly grim as one between Bernadette and the girls in Season 5, Episode 22, “The Stag Convergence.” As Bernadette celebrates her bachelorette party with Amy and Penny, she delightfully tells them about her wedding website with Howard, which contains fun facts about their families. One such fact, Bernadette reveals, is that their families used to be neighbors in Poland.

Penny’s initial reaction is “Oh, that’s cool!,” until Amy interjects with “No it’s not, I’ll explain it to you later.” The show never reveals Amy’s explanation, but what adult viewers can glean from this fact is the strong possibility that during World War II, Bernadette’s Polish-Catholic family ratted out Howard’s Jewish family to the Nazis. It could also be implying that Bernadette’s family were actually Nazis, while Howard’s family were prisoners in neighboring Auschwitz, the notorious concentration camp. 

Thankfully, the only thing disproving this possibility is the fact that there aren’t any other references throughout the series to Howard’s family suffering in the Holocaust. Adult viewers may be sensitive to any types of jokes referencing that global tragedy, but for now, it’s not among the scenes in “The Big Bang Theory” that upset fans the most. 

Mayim Bialik may be mostly known for her role as Amy Farrah-Fowler, but her career transformation from childhood to “The Big Bang Theory” wasn’t without its notable moments. After several years of being a child actor, Bialik’s breakout role actually came in the ’90s, when she was cast as the lead in the NBC sitcom “Blossom” at 15 years old. “Blossom” remained one of the most influential sitcoms of the ’90s, even after Bialik grew up and pursued a doctorate in neuroscience, which all preceded Amy’s introduction on “The Big Bang Theory.” 

In fact, Bialik was such a celebrity by the time the first season of “The Big Bang Theory” arrived that she was referenced by the characters in Episode 13, “The Bat Jar Conjecture.” While brainstorming a fourth member for their Physics Bowl team, Raj suggests “the actress who played TV’s Blossom” due to her Ph.D. It’s also an ironic reference considering a young Johnny Galecki also guest-starred on “Blossom,” meaning that Leonard and Amy were each other’s first on-screen kiss. 

Even after Bialik joined the cast of “The Big Bang Theory,” the references to “Blossom” didn’t go away. In the Season 6 episode “The Holographic Excitation,” Amy and Sheldon debate a couples costume for Halloween, with one of Amy’s suggestions on their shared Venn diagram being “Blossom and Joey” — a fun Easter egg for older viewers who grew up watching Bialik’s previous sitcom. 

Even diehard “The Big Bang Theory” fans may not realize that every episode of the show features a vanity card at the very end written by series creator Chuck Lorre. This is a trend that exists for all of Lorre’s television shows on CBS, including “Young Sheldon,” “Two and a Half Men,” and “Mom,” and they’re always different. Often, they contain Easter eggs for the episodes themselves, or completely unrelated messages to the audience, but only adult viewers will probably have the patience to notice and read every single one.

Oftentimes, these vanity cards end up censored either by CBS or Lorre himself, but are made available to read in their uncensored forms on his website. In Season 6, Episode 6, for instance, “The Extract Obliteration,” the uncensored vanity card contains a profanity-laden rant from Lorre about gun violence and racial issues. During Donald Trump’s first term in office in particular, Lorre’s vanity cards were remarkably political and rebellious. 

For a show with lots of Easter eggs on-screen, Chuck Lorre’s signature vanity cards are proof that the minds behind this show were trying to cater to a much more adult and intelligent audience than the massive one of all ages it had. At the very least, “The Big Bang Theory” still has something for everyone to enjoy.