When the terrifying, gargantuan shark first appears, Roy Scheider’s character memorably responds with, “You’re gonna need a bigger boat.”

According to The Hollywood Reporter, the actor ad-libbed the famous line, which was based on something the production team said to each other on set in reference to their “stingy producers.”

Screenwriter Carl Gottlieb told the publication that the actor actually tried to put the line into the film in a few different spots.

“It was so appropriate and so real,” he said. “And it came at the right moment, thanks to Verna Field’s editing.”

On the season three episode of the NBC show, “Gay Witch Hunt,” Oscar Martinez’s shocked response to Michael Scott kissing him on the lips is totally authentic.

“… He wasn’t supposed to kiss me, we were just supposed to hug,” actor Oscar Nuñez told AV Club in 2008. “And that particular take he came in really close, and I’m like, ‘Where is he going with this?’ And then I’m just thinking, ‘Oh God, nobody laugh so we can use it.’ And they didn’t, and it worked perfectly. It was a lot of fun.”

Director Todd Phillips said that he played the film's score for Joaquin Phoenix because he "wanted the music to affect and infect the set in a way." During the first take as the score was playing, Philipps revealed that "as Joaquin is struggling with Arthur's smile, this little tear appears, and we just had the scene and we moved on."

Edward Norton explained he really hit Brad Pitt in the ear during one of the scenes.

“It’s the first punch in the movie and I hit him in the ear,” said Norton.

“[Director’David) Fincher came up to me and said, ‘Hit him, connect with him somewhere.’ I didn’t know what to do and I hit him in the ear.”

And Brad Pitt was just as surprised.

To ensure that the cast of kids gave realistic expressions of horror as they first discover Pennywise (Bill Skarsgaard), the horrible clown monster, the directors made sure they had no idea what he looked like, and kept Skarsgaard separated from them.

The kids didn’t see images of the clown until they filmed the projector scene. Finn Wolfhard and his fellow actors watched the screen and the clown appear for the first time. Their growing horror and final shock was as real as the audience’s.

The Exorcist was a shockingly twisted thriller/horror film, with some of the earliest forms of jump-scares. And in order to make sure the actor portraying Father Karras (Jason Miller) got a proper look of revolted horror, the director told him the pea-soup vomit spat up by Linda Blair would strike him in the chest. (And yes, it was really Anderson’s pea soup, mixed with a bit of oatmeal.)

Instead they directed the barf-nozzle right into his eyes, giving a nasty pea-soup surprise to the actor. At least he looks convincingly freaked out (and annoyed) at the demon possessing Regan (Blair).

One scene has the slowly-losing-his-mind protagonist finding himself smack dab in the middle of Times Square wearing only his undergarments. If you thought there were way too many people there for all of them to be extras, well – you were right! Those are real people who happened to be there at the time, hence their freaking out at seeing a movie star in his tighty whiteys.

This sounds like a major HR issue, but Friedkin said he only ever fired blanks because he found it difficult asking actors to portray certain emotions without them looking corny or unbelievable. According to Friedkin, he got the idea after reading an article about George Stevens and didn't think it was that big of a deal.

In one scene Kevin kisses Archie, it was totally unscripted and leaves a shock on everyone elses faces

Hedren was originally told that the birds would be fake, but there were mechanical issues, so real birds had to be swapped in. Upon visiting the set and seeing the filming circumstances, Cary Grant said to Hedren: "You’re the bravest woman I’ve ever seen."

The bleakness of the film is underlined in a scene where a group of schoolboys (including Bradley) are caned by a teacher. Their reactions of startled pain are very real, as Loach has promised they’d cut right before they’d be struck… but instead he kept the cameras rolling as the child actors were, in reality, hit by the cane