There are plenty of things fans know and love about The Big Bang Theory. From all the lyrics of the iconic theme song to every character's catchphrase, like Sheldon's "Bazinga!", fans can't get enough of TBBT. However, some fans go beyond the surface of what each episode shows and dig deeper into their favorite sitcom to find out more about it and the characters they love.

Most fans pick up special details about the show after rewatching it several times, while others find extra information about their favorite scenes or character idiosyncrasies from a deep dive on the Internet. Whether it's the inspiration behind Sheldon's and Leonard's names or the exact number of men Penny dated on the show, there are some things only true-blue The Big Bang Theory fans would know.

Updated on September 7th, 2022, by Lynn Gibbs: The longer The Big Bang Theory has been off the air, the more time fans have to learn more about all that went into its creation. Between the tell-all book The Big Bang Theory: The Definitive, Inside Story of the Epic Hit Series coming out this October to ongoing interviews with the cast and crew, there's a lot to learn about this beloved sitcom that isn't widely known.

The Show Had Two Pilot Episodes

The show's official pilot episode aired in 2007 and launched the wacky world of Sheldon, Leonard, and their smart friends.

However, not every fan knows that before the episode that introduced them to Penny during her first meeting with the guys, there was another pilot that didn't make it to the screen.

The unaired pilot of TBBT is quite different, compared to the official one. For example, Penny isn't present and in her place is a character named Katie who meets the guys for the first time. She's wildly different from the sweet, perky girl-next-door Penny was and in addition, that version of the pilot didn't have Raj or Howard.

Scientific Advisors Are On Set

Since science is a large theme in the show and it's widely talked about and dissected in most episodes, production needed scientific advisors on-set to make sure the theories, principles, and math work they were doing was scientifically sound.

With Sheldon as one of the more intelligent characters on TBBT, the writers needed Jim Parsons to nail the understanding and delivery of most scientific topics. Science noted that astrophysicist David Saltzberg was one of the few consultants on the show.When asked about his work on the show, Saltzberg said "The writers and I used to have to go back and forth a lot more for me to converge on what they wanted.

But now we just finished 7 years together, and so we're a little bit like an old married couple. We know each other's thinking a little better."

There's A Reason Penny Started Bartending

In season 4, Penny asked the group if she could practice making them cocktails because she was training to be a bartender at the Cheesecake Factory. The Cheesecake Factory had some of the funniest moments on TBBT, so fans were excited to see how Penny's bartending skills played into it.

According to Express, Kaley Cuoco (Penny) broke her leg horseback riding.

With a cast on, the writers had to find a way to cover her legs during work — which is where the bar top came in handy.

Take A Close Look At Leonard's Glasses

Leonard's transformation throughout TBBT was a slow one. It took him years to become confident in himself, and even when he married Penny and became more secure in his job, fans were bothered by how whiny and unsure he was.

The one thing that didn't change too much was Leonard's sense of style. In fact, if viewers took a close look at Leonard's face they'd notice that he didn't have glass in his glasses.

In an interview with Huffington Post, Johnny Galecki said it was his choice for Leonard to wear glasses. The only problem was that he forgot they didn't have lenses in them and he once rubbed his eyes through his glasses without realizing, which ruined the shot.

Raj Was Inspired By A Real Person

Although Raj was shy and intimidated by women or those with a strong presence, he was a beloved character that fans rooted for. Funny enough, Good Housekeeping shared that Raj was based on a real person.

The site shared that executive producer Bill Prady based Raj on an "old coworker" who had similar issues talking to women. He, too, needed a sip of alcohol to be relaxed enough to speak to a beautiful woman. Thankfully, Raj got over his fears and was able to speak to those without the introduction of wine or beer.

An Error In The Opening Credits

Diehard fans love the theme song to The Big Bang Theory because it's specific and original to the series. However, there's one thing that fans missed during the theme song and introduction.

Yahoo shared that the timeline that scrolled throughout the intro has an error in it. Instead of saying 91,000 BC, it actually says 91,000 9C. The next time fans binge the series, take a hard look at the intro to see the error!

Mayim Bialik Actually Has A Ph.D. in Neuroscience

The core characters on The Big Bang Theory had a background in science (except for Penny), with a majority of them holding Ph.D.'s in their respective fields, apart from Howard who was always teased by Sheldon for only having a master's degree.

Beyond the screens, however, only Mayim Bialik (Amy Farrah Fowler) has a Ph.D. in neuroscience, similar to her character on the show.

Thanks to this qualification, Bialik fit perfectly into the world the creators crafted of science and nerd culture. According to CheatSheet, she also fact-checked the scientific concepts mentioned on the show that were related to neurobiology.

Leonard & Penny Both Proposed To Each Other Three Times

The iconic Leonard and Penny relationship story is one of the most prominent storylines throughout the show, from season 1 to the finale.

They went from simply being neighbors across the hall to being married and expecting their first child 一 with lots of drama in between.

One of the most memorable things about their relationship that some fans might not have noticed was that between the two of them, the couple had a total of six proposals. The first was Leonard's fake proposal during their Valentine's Day date in 'The Tangible Affection Proof,' followed by his mid-coitus proposal in 'The Launch Acceleration.' Penny proposed for the first time in 'The Hesitation Ramification,' and again during a funeral in 'The Proton Transmogrification.

' When they officially got engaged, Penny was the first to suggest that they get married and Leonard followed it up by presenting her with a ring from his wallet.

Raj Spoke Twice In Front Of Penny Without Alcohol

For the first few seasons of the show, Raj couldn't speak in front of women. It was one of the saddest things about Raj. He later discovered he could do so once he had alcohol and eventually, he could speak to ladies all on his own. In fact, Penny was the first woman he managed to speak to, both, while drunk and without sipping alcohol.

A few fans will remember that 'The Bon Voyage Reaction,' wasn't actually the first time Raj spoke to her without drinking first.

In season 1's 'The Dumpling Paradox," Raj made a snide comment to Leonard while Penny was in the room, and in 'The Bat Jar Conjecture,' he made a comment to Penny before clapping his hands over his mouth. While the first incident was believed by many to be an oversight, it seemed to be setting up Raj's breakthrough with a woman he slowly got comfortable with over the seasons.

Raj Dated 13 Women On The Show

Raj's woes with love were no secret, and out of all his friends, he seemed to be the most unlucky when it came to affairs of the heart. By the end, he was the only one in the group who wasn't married or having a baby. Even Stuart, who had formerly been his fellow single wingman was dating Denise. However, Raj's single status was certainly not for a lack of trying.

Raj had relationships with 13 women. This included ladies he only had one date with, one-night stands, and a girlfriend he mentioned in passing. That list includes the lady from Penny's Halloween party in 'The Middle Earth Paradigm,' Abby (Danica Mckellar), the one he hooked up with at a bar in 'The Hofstadter Isotope,' the girlfriend he mentioned in passing in 'The Desperation Emanation,' Lalita, Emily, Lucy, Emily Sweeney, Claire, Isabella, Ruchi, Nell, and Anu.

Bernadette's Real Voice

Bernadette was known for many things on The Big Bang Theory; from her ability to switch between super sweet and super mean effortlessly to her highly squeaky voice. Her voice was the subject of many jokes and gags on the show, but some fans will be surprised to know it's actually an act.

According to TheThings, Melissa Rauch made Bernadette's voice squeaky intentionally to make the character more fun, and the high-pitched tone was inspired by her mother.

Rauch's actual voice is wildly different from her character's. Bernadette's attitude aged poorly, but her voice didn't.

The Mystery Of Penny's Last Name

While TBBT often left certain B-plots hanging, there were also some major plot points that were never explored. One of these was Penny's last name, which was never mentioned on the show; not even when her family came for her second wedding.

According to one Reddit user Quell_Alma, Penny's last name may have been revealed fleetingly during 'The Work Song Nanocluster' on the package she received, which was addressed to Penny "Teller.

" The image is quite blurry, so it's hard to tell if this is actually accurate. However, according to an interview at WonderCon, the producers said they would never reveal Penny's last name on the show.

Amy Was Mentioned On The Show Before Appearing On It

While looking for a fourth person to join their Physics Bowl group in 'The Batjar Conjecture,' Raj suggested Bialik, whom he called TV's Blossom, and "the girl from the Wonder Years," Danica Mckellar, who played Abby in 'The Psychic Vortex.

' It was a fleeting comment that many overlooked until the two ladies appeared on the show.

Amy joined the show two seasons later in 'The Lunar Excitation,' and eventually became a series regular. Not a lot of people remembered that small detail, but it was a neat call back to a seemingly random comment.

Each Character Had A Signature Look

One small detail that set the characters apart was their dress code. Each had a certain preference when it came to clothing, from Sheldon's two T-shirts to Amy's knitted cardigans and Bernadette's cardigans and floral dresses.

Leonard's signature look was hoodies, Raj preferred sweater vests, and Howard leaned towards dickies, tight pants, and statement belt buckles. Penny was the only one of the main group who didn't have a specific preference but was always one of the best dressed characters.

Sheldon's Number 73 T-Shirts

Although Sheldon did wear some impractical outfit choices on TBBT, he relied on a few staples. On several occasions, Sheldon was seen wearing a different-colored shirt with the number 73 on it. In the episode 'The Alien Parasite Hypothesis,' he even explained why 73 was the best number.

According to CBR, the number 73 was actually a nod to actor Jim Parson's birth year (1973), which they incorporated onto his shirts. As one of the main characters, this was a cool way of adding a piece of the actor to the character.