Given its lengthy run of 12 seasons and 279 episodes, it only makes sense that the cast had to follow certain rules behind the scenes in order for Chuck Lorre's show to flow properly.

In the following, we'll take a look at some of the major rules, and how the cast rarely broke them from time to time. One of the rules deals with the appearance, in which Kaley Cuoco boldly decided to break without telling anyone. In addition, we'll reveal another rule even the main stars didn't break, which was manipulating the script and improvising certain scenes.

This was a rarity on The Big Bang Theory, however, once again there are exceptions.

And one improvised scene in particular resulted in high praise and more episodes for a certain recurring character. Let's take a closer look.

The Big Bang Theory Cast Had To Be Careful Altering Their Appearance Outside Of The Show

The cast of The Big Bang Theory had a few rules they needed to follow. Among them, was being very careful in relation to their appearances. Rarely did the main cast of men on the show grow beards, and instead, they took advantage when the show was filming, in particular Kunal Nayyar and Johnny Galecki who would both grow lengthy beards when the cameras of the show weren't rolling.

There was a major exception, however. Kaley Cuoco showed up to The Big Bang Theory set for season 8 with an entirely different look. Chuck Lorre revealed nobody was told, while Cuoco revealed she did it for the independent film, Burning Bodhi.

Cuoco didn't get into trouble for it, but she did regret the entire change.

"I just cut my hair off and didn't tell anyone. I did it for an independent film called Burning Bodhi, and basically showed up to our Big Bang wrap party with short hair. [Cocreator] Chuck [Lorre] hugged me and said, "Wow, look at your hair!" and I said, "Do you like it?" I don't know if I was being rebellious.

I mean, I did do it for the movie, which was my excuse to cut it."

"At that point we were heading into our eighth season and something needed to shake up. I was bored and sick of the hair, and what's funny is I thought by cutting my hair, I would spend less time in the hair and makeup chair, even though I loved the hair and makeup team."

Cuoco revealed her decision did not save any time and instead, it just caused more time in the makeup chair trying to perfect her new look...

The Big Bang Theory Cast Always Followed The Script, But There Were Exceptions, Notably Kevin Sussman

The Big Bang Theory cast did not improvise during the filming of the show, and following the script was an important rule everyone needed to follow, especially given how tight the shooting day were. However, there are some exceptions. The most notable of the bunch was Kevin Sussman.

Early on during his time with the series, Kevin Sussman quietly says, "I love you" under his breath during a scene with Penny at the comic book store. The creators of the show not only loved this moment, but they also added to Sussman's involvement following the hilarious scene.

Still, despite the organic moment, Sussman revealed alongside TV Store Online that he was still always inclined to stick to the script.

"The cast doesn't improvise. Because we don't need to, the writers are so good that if a joke doesn't hit, the writers will converge on the spot and within three minutes have it rewritten—so it is funny."

Jim Parsons had another great moment on the show. He threw his roommate agreement papers in the air and one of them just happened to land on his head. Thankfully, the show kept the hilarious moment, while Johnny Galecki was somehow able to keep a straight face.

Kunal Nayyar And Others Revealed Why They Never Touched The Script

Main cast members Kunal Nayyar and Simon Helberg discussed improvising on the series. Although it might seem like they did at times, that was not the case. Nayyar revealed that the shooting schedule was way too tight, and there wasn't time for it. While Simon Helberg added that the script just didn't need to altered given how on point it always was.

"The writers write and the actors act. I've worked very differently before.

There are a lot of changing lines while we're taping, and coming up with jokes, punching it up and rewriting scenes."

"My impulse is always to try to contribute, but very quickly, I felt that that wasn't necessarily the way that this show worked. In some ways, it's a great harmony. They are fantastic. It does take a little bit of courage to say, "Hey, how about this?," but that's just because they're so great at what they do."

Clearly, the showrunners and writers had to magic formula behind the scenes, as the cast was very content with their circumstances.