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Allow us to apologize in advance because we’re about to break the first rule of Fight Club which is: You do not talk about Fight Club.

Released in 1999, the movie starring Brad Pitt and Edward Norton initially received mixed responses from critics, but is now considered one of the greatest movies of the 1990s.

To celebrate this classic film, we’ve tracked down some of the best little-known facts about "Fight Club."

CASTING

According to Chuck Palahniuk, whose book the movie is based on, Brad Pitt and Edward Norton’s parts were decided quite early on.

But that wasn’t the case with the character that ended up being played by Helena Bonham Carter.

“At the time Courtney Love was going out with Edward Norton and she was really campaigning for that part, so I had assumed that she would play Marla,” Palahniuk told Men’s Health.

“But David [Fincher] did so not want to cast her. He wanted to cast against type and that’s why he was advocating Helena.”

Director David Fincher has also said that he offered the part to Julia Louis-Dreyfus who was famous for playing Elaine Benes on "Seinfeld." But the meeting didn’t go to plan.

“She had no idea who I was,” Fincher said, according to Total Film.

“I’m sitting there thinking of myself, ‘My God, you are such a f-----g loser.’ I think she’s amazingly talented, I just thought she was too young. When you realize Tyler doesn’t exist and The Narrator’s been abusing Marla himself, it needed to be somebody who, for lack of a better explanation, was there out of choice; not somebody who didn’t know any better.”

SICK STAR

Bonham Carter had to smoke so many cigarettes in the movie that she actually got sick from it.

“At the end of the shoot I gave Fincher an x-ray of my lungs,” the actress told Total Film.

“I had to have an x-ray because I got bronchitis — surprise, surprise — during the six months of filming. And Fincher does so many takes and lots of smoke shots.

“He got obsessed with the smoke. It had to float in a particular way. So I was just always sitting there in a cemetery of cigarette butts.”

SALARY DIFFERENCE

Pitt was paid seven times more than his co-star, Norton.

Pitt received $17.5 million for his role in Fight Club whereas Norton pocketed $2.5 million.

STARBUCKS CUPS

We all noticed Brad Pitt’s ripped torso, but few of us noticed there’s a Starbucks coffee cup in EVERY SINGLE SCENE. Fincher explained why to Empire magazine.

“When I first moved to LA in 1984, you could not get a good cup of coffee in Los Angeles to save your life,” the director said.

“Then Starbucks came out, and it was such a great idea: good coffee. And when it became successful there were like two or three on every block. It’s too much of a good thing.

“But [Starbucks] read the script, they knew what we were doing, and they were kind of ready to poke a little fun at themselves. I mean, they wouldn’t let us use their name on the coffee shop that gets destroyed by the piece of tragic corporate art, but they were willing to give us the rest of their stuff.

“We had a lot of fun using that — there are Starbucks cups everywhere, in every shot. I don’t have anything personal against Starbucks. I think they’re trying to do a good thing. They’re just too successful.”

OFFENSIVE LINE

In the original script, there was a line that Marla was meant to say to Tyler after they have sex for the first time.

The line was, “I want to have your abortion."

But the Fox 2000 Pictures president of production, Laura Ziskin, found the line horribly offensive and pleaded with Fincher to change it.

“I’m begging you, please. It’s too offensive. You have to take it out,” she said to the director.

He agreed, on one condition.

“I will shoot something else to replace that line, but you have to promise me that I have the final say on whatever that is. I get to come up with the replacement,” Fincher said to Ziskin.

She agreed and Fincher changed the line to, “Oh my God, I haven’t been f----d like that since grade school."

When Ziskin found out about the new line she hated it even more than the original and begged Fincher to use the abortion line, but a deal’s a deal.

INJURED STARS

There are a lot of fight scenes in the movie and the fact that David Fincher likes to shoot a lot of takes meant that some of the stars picked up injuries during the physically demanding scenes.

Both Pitt and Norton hurt their thumbs and ribs and the Norton also picked up a nasty head injury.

“There’s a shot in the movie where Brad throws me through the toll booth of a parking lot and I crawl under a car,” Norton recalled to Total Film.

“It’s an elaborate shot and Fincher wanted to do it all in one. So we did it a lot of times. Like a lot. Like 20 or 25 times. I remember going into a head state of like, ‘F--k it. I can do as many as he wants me to, because there’s no going back now.’

“Eventually Brad started getting uncomfortable, around 33 or 34, and he said, ‘Look, seriously, no more. He’s really getting beat up!’ Fincher just goes, ‘Last one, I swear! Last one!’

“So I went crawling under the car as hard as I could and I was too tired and I didn’t duck enough and I really rang my head hard against the transmission and sort of screamed and he jumps up and goes, ‘That was the one!’”

JARED LETO

There’s a scene in the movie where Tyler is talking to the Fight Club members and says: “We’ve all been raised on television to believe that one day we’d all be millionaires and rock stars. But we won’t.”

As he says the words, “rock stars,” Tyler stares directly at a character called Angel Face who is played by Jared Leto aka an actual rock star.

This article originally appeared on news.com.au.