QUIZ: How Well Do You Remember “The Big Bang Theory?”

Much to Sheldon’s horror, his mother and sister often refer to him as Shelly, a nickname that was first mentioned on the episode “The Luminous Fish Effect" in season one.

Leonard wasn’t too upset. But what viewers found odd about the situation was that Penny had thrown Leonard a birthday party in season one and the episode in question happened about six years later. So it didn’t make sense that she had forgotten his birthday.

Known best for her role in “The Good Wife,” Baranski first appeared as Leonard’s mom in season 2, episode 15 and continued to recur as the high-strung character until the end of the series.

Chuck Lorre initially didn’t want to cast Jim Parsons for the role because he thought he was too good at his audition. After Parsons finished his audition, Bill Prady, who co-created the show with Lorre, turned around and told Lorre “That's the guy!” to which Lorre said, “Nah, he's gonna break your heart. He'll never give you that performance again.” Boy where they wrong, huh?

The “Home Alone” star admitted he was approached three times to play a role on the show, (but he never specified who he would’ve played). Apparently, the plot didn’t resonate with Culkin, who told the producers to take a hike. He said, “I said no. It was kind of like, the way the pitch was, ‘Alright, these two astrophysicist nerds and a pretty girl lives with them. Yoinks!’ That was the pitch. And I was like, ‘Yeah, I’m cool, thanks.’”

Believe it or not, the original title of the show was supposed to be "Lenny, Penny, and Kenny." Yikes! We know! During an interview with TV Insider, Cuoco confessed she had originally auditioned for the role of Katie which was part of the unaired pilot, but she wasn’t cast because she was too young at the time.

The creators decided to keep Penny’s last name a total mystery throughout the series. But unbeknownst to fans, Penny’s last name was revealed in season two. When she married Leonard, she became Penny Hofstadter, but her maiden name was Teller. This is revealed in season 2, episode 18, when Sheldon delivers a box of supplies where you can clearly see her full name.

The writers didn’t actually base the character on a condition or syndrome. Due to his anti-social manners and “Sheldony” ways, most viewers assumed Sheldon Cooper had Asperger's syndrome. But the creators have a different take on that, saying, "We write the character as the character. A lot of people see various things in him and make the connections. Our feeling is that Sheldon's mother never got a diagnosis, so we don't have one.”

Aside from having flawless comedic timing, most of the cast members are highly skilled musicians. Jim Parsons and Mayim Bialik took the time to learn how to play the harp and the theremin for the show, while Johnny Galecki has played the cello from a very young age.

Soft Kitty is a song that dates back all the way to the 1930s. Well, sort of! According to a copyright lawsuit, the children’s song “Warm Kitty” which was written by Edith Newlin, appeared in the book "Songs for the Nursery School" which was published in 1937.

We can’t imagine anyone other than Mayim Bialik as Amy, but actress Kate Miccuci, who plays Raj’s shy girlfriend had originally auditioned to play Sheldon’s girlfriend. The awkwardness was there, but the role didn’t quite suit her. Eventually, she landed the role of Lucy.

For 12 seasons, Sheldon used this catchphrase whenever he wanted people to know he was pranking someone.

The trio had reportedly been making around $300,000 per episode, but after striking a deal with CBS, the actors got a lucrative bump in their salaries and they reportedly made about $1 million per episode.

As you can imagine, the show about a group of brainy science nerds attracted a plethora of big name celebs and some of the greatest minds of the 21st century, including Bill Nye the science guy, Microsoft’s creator Bill Gates, CEO of Tesla Motors Elon Musk, and astronaut Buzz Aldrin.

Despite the many fictional entanglements and on-screen romances, the only actors who actually dated their co-stars were Kaley Cuoco and Johnny Galecki, who dated for two years.

Sheldon dedicated an entire video podcast to teach people how to properly fold flags and handle them.

The show filmed 2 different pilots because the first one was sort of a flop. Still, CBS thought it had potential, so Lorre and Prady gave it one more shot and it was a big bang, indeed.

Some believe the feud started when Wheaton failed to attend the 1995 Dixie Star Trek convention, which left Sheldon angry after he rode the bus for 10 hours to meet him. Throughout the show, Wheaton was always one upping Sheldon, which explains why there was so much animosity.

Producers of the show didn’t have a profession set in mind for Mayim Bialik's character, but when she joined the cast, they decided it would be a smart move to make her career be the same as the actress who played her.

Both Sheldon and Leonard work at Caltech and live together in Pasadena, across the hall from Penny. Their apartment is located in the fictional address 2311 North Los Robles Avenue.

In the pilot, Penny works at Cheesecake Factory as a waitress to support herself while she waits for her big break as an aspiring actress.

According to fans, when Sheldon’s angry, he wears a red t-shirt. When he’s calm and feeling fine, he wears green, and when he wears light blue, it’s because he’s feeling hopeful.

The song is composed and performed by the iconic band "Barenaked Ladies." Unfortunately, the song resulted in a lawsuit due to its use on the show, because one of the band's members believed that they weren't properly paid for its use.

A long time ago, way before the show was picked up, co-creators Chuck Lorre and Bill Prady originally wanted Galecki to play Sheldon. The actor told Larry King, “they came to me with the idea of playing Jim Parsons' character, the Sheldon character. This is long before they had met Jim and before anything was even written.”

Sheldon Cooper wouldn’t be the Sheldon Cooper we know and love without Jim Parson’s brilliant take on the character. After his audition, Chuck Lorre said, “He was astonishing, I didn't even believe it when it happened. I never anticipated the character being the way he crafted it. It was funny, it was touching, it was real.”

The successful spin-off follows the life of a young Sheldon Cooper. The show focuses on his childhood and how Sheldon struggles to balance being a bona fide genius while trying to fit in with other kids.

Yup! Raj’s apartment and Howard and Bernadette’s home are located in the same set, therefore, it would be a major hassle having to redecorate and switch up the furniture for just one episode.

Despite the fact that Penny and Leonard had a few bumps on the road of their relationship, viewers only saw them break up once. They got back together after Leonard called things off with Priya.

During the accident, a horse tried to jump over Cuoco and it stomped on her leg and broke it. But like a real trooper, she returned to work after a two-episode absence, but had to spend a lot of time behind a bar counter so viewers wouldn’t notice she broke her leg.

When Leonard originally brought up the subject, she told Leonard that she wasn’t sure if she wanted to have kids, which concerned Leonard as he wanted to have kids. But towards the end of the series, viewers learned that Penny was pregnant and was actually happy about it.

Actor Johnny Galecki, who played Leonard, had to remove the lenses because Jim Parsons is taller than him. So, whenever he looked up at him, the lenses would reflect the set lights which ruined the shot.

Leonard confessed to Penny that he slept with someone else. Although Penny was initially thrown by the confession, she forgave him because they hadn't gotten engaged yet.

Best known for playing Geordi LaForge on “Star Trek: The Next Generation,” Burton has guest-starred several times on “The Big Bang Theory” during seasons 4, 6 and 8. In one episode, he appeared on Sheldon’s YouTube show “Fun With Flags” to talk about “Star Trek” flags.

In fact, Parsons had never seen a single episode of “Doctor Who” or “Star Trek.” He actually wasn't much of a sci-fi fan at all. But he did an amazing job of fooling audiences into thinking that he was his alter ego, Sheldon Cooper.

On the sitcom “Roseanne,” Sara played Darlene Conner, who was also the girlfriend and eventual wife of Johnny Galecki’s character David Healy. Sadly, when the “Roseanne” revival aired, viewers learned that David and Darlene had broken up.

Penny used the same purse throughout most of the series. In fact, the purse viewers saw her with since the second episode of the first season is the same purse they see her with all the way up to the final episode.

Although she was just a recurring character, she played a very important role on the show as Sheldon’s mother, Mary Cooper. Her first appearance was in episode four of season one.

Long before “The Big Bang Theory,” Mayim Bialik, who played Amy, had her own show called “Blossom.” And during one episode, Johnny Galecki, aka Leonard, guest starred. In fact, it was one of his first roles on television.

He appeared in season two, episode four as himself. In the episode, Raj runs into Sheen at a bar and tells him he’s going to be on the pages of People magazine. But viewers will also note that Sheen was also starring on another Chuck Lorre series called “Two and a Half Men” at the time.

Blossom and Joey were brother and sister on the 1990’s show “Blossom,” where Mayim Bialik played Blossom. Joey was played by dreamy actor Joey Lawrence. The writers wrote that line as a salute to Bialik’s time on the show.

In the episode “The Fish Guts Replacement,” Sheldon Cooper shared that his favorite animated theme song was from the popular cartoon “Teenage Mutant Ninja Turtles,” which was written by “The Big Bang Theory” creator Chuck Lorre.

When viewers saw Sheldon Cooper playing the musical instrument known as a theremin, they were actually listening to actor Jim Parsons playing it. It turns out that he can play this instrument that doesn’t require physical touch to play.

The “Terminator: The Sarah Connor Chronicles” actress is best known for her role as the reprogrammed Terminator Cameron who goes back in time to save John Connor. Well, in season 2, episode 17, the guys from “The Big Bang Theory” run into Glau on a train and try hitting on her; except for Sheldon, of course.

In 2012, biologists identified a new species of bee which they named Euglossa Bazinga. The name was chosen in honor of “The Big Bang Theory.” Now hardcore fans will recall that Bazinga was Sheldon’s catchphrase, but he was also deathly allergic to bee stings.

Missy was played by actress Courtney Henggeler, and she was Sheldon’s twin sister. But she was not a total brainiac like her brother, and yet that didn’t stop her from being proud of Sheldon’s achievements.

A TV show called “The Theorists” aired in Belarus and it was a total knock-off of “The Big Bang Theory” in the United States. For one thing, they had a blonde neighbor who looked a lot like Penny. They also had two characters named Sheldon and Raj who were scientists along with two other friends named Leo and Hovart.

Known best for her role as Starbucks on “Battlestar Galactica,” Katee appeared in the same uniform she used on the sci-fi series during one of Howard’s fantasies. She later appeared with him in the bathtub. But it wasn’t a one time gig. The actress has appeared in season three and season four episodes.

In the 100th episode, we see Penny wearing the exact same top that she had on in the pilot episode. Coincidentally, this was the episode where Leonard asked Penny out again after the two lovebirds had taken a break.

While most Buffy fans know her as Faith, the rogue slayer who went bad in season three but eventually had a change of heart, Eliza played FBI agent Angela Page in season 4, episode 7. Page’s role was to interview Howard and his friends to see if he was qualified to get the proper clearance to perform government work.

Chuck Lorre posts a series of vanity cards during the end credits of each episode that are either goofy and funny or just downright serious. But he doesn’t just do this on “The Big Bang Theory.” He incorporates these vanity cards in the end credits of other shows he produces, too.