1. Raiders of the Lost Ark – Indy Brings a Gun to a Knife Fight

It might be easy to imagine shooting a movie as something of a luxury. But according to producer Frank Marshall, Raiders of the Lost Ark, the first Indiana Jones film, was shot in “Tunisia, in 130 degrees for six weeks and we had three days left. We were supposed to shoot this huge fight between the whip and the sword.”

The previous nearly month and a half of filming seemed to have taken its toll on the film’s star, Harrison Ford. Rather than spend an additional three days shooting yet another physical fight scene, Ford simply pulled out his prop gun and pretended to shoot his adversary. As Marshall described it, “After lunch we did three shots…and it’s the biggest moment of the movie.”

2. The Silence of the Lambs – The Hiss

Screenwriter Ted Tally won the Academy Award for Best Adapted Screenplay for his adaptation of The Silence of the Lambs from book to film. But there was one memorable part of the film that Tally didn’t write. It happens when Anthony Hopkins’ imprisoned cannibal psychiatrist Dr. Hannibal Lecter is being interviewed by Jodie Foster’s character Clarice Starling. While mentioning he ate a patient’s liver (“with some fava beans and a nice Chianti”), he suddenly slurps or hisses.

It’s an on-screen moment was totally improvised by the accomplished actor. Judging by the look on Clarice’s face, it was inhumanly unsettling. According to Tally, it seemed like no other actor could accomplish that: “I couldn’t think of an American actor who could really do it without us seeing quotation marks around everything he said…he’s smart. You can’t fake that smartness on a big screen.”

3. Taxi Driver – You Talkin’ to Me?

The line listed in the Hollywood Reporter as one of the 100 favorite movie quotes of all time wasn’t even written in Taxi Driver’s original script. But, according to an interview with the cast at the 2016 Tribeca Film Festival, director Martin Scorsese recalled asking his lead actor Robert De Niro, “Can you say something to yourself? In the mirror?”

Once the cameras were rolling, De Niro looked in the mirror and repeated to himself, “Are you talking to me?” It seems as though De Niro doesn’t enjoy repeating it time after time. Before the Tribeca Film Festival, De Niro decided that he would allow the crowd to get it out of their system once by leading them in a shout of, “You talkin’ to me?”

4. The Shining – Here’s Johnny!

At the height of The Shining‘s drama, tension, and terror comes an unforgettable moment when a possessed Jack Torrance, played by Jack Nicholson, puts an ax through the bathroom door that his wife is hiding behind. While his wife, played by Shelley Duvall, is screaming, Nicholson suddenly shouts some unscripted dialogue which became one of the most memorable lines of the film — “Here’s Johnny!”

Although the line was improvised in the moment, it was inspired by the popular cultural fixture, the late-night show The Tonight Show Starring Johnny Carson. Reportedly, Nicholson had been pumping himself up before the scene and may have been caught up in all the energy and excitement. Even more surprising was that director Stanley Kubrick almost chose not to include it.

5. Midnight Cowboy – Taxi Incident

Anyone who has taken a trip to New York City, or even talked about a trip there with friends, has probably heard this infamous line, said in a thick New York accent, “I’m walking here!” What many people don’t know was that this line was completely improvised and occurred after a mistake on set.

While Dustin Hoffman and Jon Voight were busy trying to nail their scene of them walking down the street in Midnight Cowboy, a cab whose driver had apparently decided to ignore the “Street Closed for Filming” sign decided to drive right into the shot. Although Hoffman stayed in character, according to an interview in the National Post, “What was going through my head is: ‘Hey, we’re makin’ a movie here!'”

NEXT: These upcoming scenes were unplanned but managed to be absolutely hilarious.

6. The 40-Year-Old Virgin – Chest-Waxing Scene

The year was 2005, the American edition of the television series The Office had just started, and Steve Carrell and Judd Apatow weren’t yet the household names they are today. After working together on the film Anchorman, Apatow approached Carrell, telling the actor he was thrilled and impressed with his improvisations on the Will Ferrell movie and would be happy to make a feature with him.

While on set for The 40-Year-Old Virgin, Carrell and Apatow decided to put The Office star’s improv skills to the test. Next time you’re watching the chest-waxing scene in this comedy film, notice the lines Carrell screams out — they’re improvised. Pay close attention to the faces of Paul Rudd, Romany Malco, and Seth Rogen. That cringing that you see, that apparently wasn’t completely acting.

7. Zoolander – But Why Male Models?

It’s one of the most tense and pivotal scenes in this Ben Stiller comedy movie. After receiving an anonymous call, Derek (Ben Stiller) and Matilda (Christine Taylor) meet conspiracy theorist and former hand model J.P. Prewett (David Duchovny), who has information regarding the use of male models for political assassinations.

Derek begins by asking Prewett, “Why male models?” This prompts Prewett to take a full minute to answer in painstaking detail. Whatever the next line was supposed to be is a mystery, as apparently Stiller forgot his line and simply blurted out, “But why male models?” Rather than cut and reset, Duchovny went with it, answering his question with incredulous disbelief, and the cut was left in the movie.

8. The Godfather – The Cat

One of the most memorable scenes in the Godfather is the very opening scene, when the gravedigger Bonasera comes into Vito Corleone’s office. It’s the day of Corleone’s daughter’s wedding, and Bonasera asks for vengeance against the men who attacked his daughter. As the Godfather considers his request, we see that he is stroking a cat sitting on his lap.

The cat, it turns out, was a particularly friendly stray that had been found in the Paramount parking lot, which had been wordlessly given to actor Marlon Brando. Even though it was unplanned, the cat later came to represent the claws that hid beneath the otherwise warm exterior of the mob boss. Unfortunately, the cat’s purring ended up muffling out some of Marlon Brando’s dialogue, forcing the actors to come back and re-record dialogue for the scene.

9. The Fugitive – Tommy Lee Jones Didn’t Care

Seeing his pursuer for the first time in the dam’s water-logged tunnels, Dr. Richard Kimble (Harrison Ford) is successfully able to grab U.S. Marshal Samuel Gerard’s (played by Tommy Lee Jones) handgun. Pointing his pistol at the federal officer, Kimble shouts, “I didn’t kill my wife!” Gerald, looking bewildered, responds simply with, “I don’t care!”

According to one of the producers of The Fugitive, Roy Huggins, the original response that Jones was supposed to give wasn’t, “I don’t care,” but rather, “that isn’t my problem.” It seemed that everyone preferred the version Jones said, and the line was changed for the final cut.

10. Being John Malkovich – Think Fast!

One night on the set of Spike Jonze’s 1999 film Being John Malkovich, things were running late and it looked like they weren’t going to finish shooting one last scene. The scene involved a vehicle passenger throwing a half-full can of beer at John Malkovich while he walked down the street — and nobody thought anyone would be able to hit him in one try.

The challenging task was eventually given to John Cusack’s writing partner, who was so good that he nailed the actor in one shot. The partner decided to add his own twist to the scene by shouting, “Hey Malkovich! Think fast!” just before throwing the can. Guess that yell of pain that Malkovich does after getting hit wasn’t all acting.

NEXT: Some of these actors and actresses’ careers came to be defined by these roles, part of which they improvised.

11. Pretty Woman – Jewelry Box

According to Pretty Woman director Garry Marshall, the scene where Richard Gere shows Julia Roberts the ruby and diamond necklace, only to shut it abruptly as she reaches for it, wasn’t totally improvised. Although unscripted, Marshall told Gere to do it, thinking that it would be a hilarious prank to play on Roberts, and something fun for the gag reel.

Marshall eventually admitted in an Entertainment Today interview that they decided to add it in at the last moment: “We put it in…and it became like the trademark of the movie.” The great thing for Roberts was that, according to some critics, this was in fact the scene that caused audiences to fall for the Pretty Woman star, which would end up launching her career.

12. The Dark Knight – Joker’s Clap

It isn’t for nearly an hour and twenty-four minutes into the film that the audience is finally given a reprieve from all the film’s gritty action. After being led to believe that Jim Gordon is dead and Harvey Dent is in custody, we finally get to see the Joker (Heath Ledger) captured and placed in police custody by none other than Gordon, Dent, and, of course, Batman.

While everyone is celebrating this apparent victory, Ledger decided on the spot to upset the scene by creepily clapping along with everyone else. Nolan, apparently seeing the potential of this moment, encouraged the crew to keep filming, changing the scene from showing a Joker defeat, to foreshadowing that the Batman villain still had a few tricks up his sleeve.

13. The Dark Knight – The Hospital Bomb Doesn’t Work

When it came time to film the scene in The Dark Knight where the Joker blows up a hospital, director Christopher Nolan didn’t want to cut corners. He wasn’t about to settle for computer-generated effects or models. He wanted his team to blow up an actual building with live explosives.

Blowing up a building meant that Nolan and his team had one chance to get their shot. So we can imagine how Nolan must’ve felt when the bombs didn’t go off as expected. Rather than cut though, actor Heath Ledger stayed in character as the Joker, looking annoyed and exasperated while pressing the detonator. It worked, the building went off, and the scene made it to the final cut.

14. Dumb & Dumber – The Most Annoying Sound in the World

Dumb & Dumber, starring Jim Carrey and Jeff Daniels, is filled with laugh-out-loud moments of hilarity and stupidity. But one of those moments in the comedy classic wasn’t something that the writers had planned and reportedly came out on the fly from the hilarious mind of Jim Carrey himself.

While driving to Aspen, Colorado with — unbeknownst to our two main characters — a gangster, Carrey’s character Lloyd asks the seemingly innocuous question, “Hey, wanna hear the most annoying sound in the world?” That horrible noise, which Daniels joins in with, was completely unscripted but was so funny that it was left in the movie.

15. Caddyshack – Cinderella Story

According to Harold Ramis, the director of the Bill Murray-driven comedy diamond Caddyshack, “We always trusted improvisation…it never felt like we were ad-libbing and winging it. It’s an actual technique and a method that allows you to create material instantly. It’s not grabbed out of thin air.”

That freedom of allowing actors to express themselves means directors relinquishing control, but it sometimes leads to cinema gold. The “Cinderella story” monologue, lasting almost a minute and a half, was entirely made up by Murray on the spot. According to Ramis, “All it said in the script is: Carl is outside of the clubhouse practicing his golf swing, cutting the tops off flowers with a grass whip.” Murray ran with that and ended up giving us a terrific and funny scene.

NEXT: See which actors and actresses are fantastic at staying in character and ad-libbing scenes!

16. Good Will Hunting – Farting Wife

Nominated for nine Academy Awards, Good Will Hunting is considered by many to be a classic, and is also responsible for launching the careers of Matt Damon and Ben Affleck. The film won the Oscar for best screenplay, but one particularly memorable scene wasn’t even part of the script.

After Will (Damon) opens up and tells Dr. Maguire (Robin Williams) that he is afraid to find out a woman he likes isn’t perfect, Dr. Maguire tells Will a story about how his wife used to fart in her sleep. The entire scene was made up on the spot by comedic stream-of-consciousness genius Williams, so we might be able to assume that Damon’s hysterical laughing at the end of the story may not have been entirely fake.

17. Full Metal Jacket – Nearly All of Gunnery Sgt. Hartman

As a teenager, R. Lee Ermey was given a choice: go to prison or join the Marine Corps. Ermey picked the latter and ended up rising through the ranks to become a drill sergeant. That experience in the Marines served him well, especially when he was cast as Gunnery Sergeant Hartman, the drill sergeant who terrifies the recruits at the beginning of Full Metal Jacket.

According to an article written by the Sydney Morning Herald, half of the dialogue from Ermey as he berates the recruits wasn’t written in any script; it was totally made up on the spot. To hear the actor discuss it himself, “My main objective was basically to just play the drill instructor the way the drill instructor was and let the chips fall where they may.”

18. The Empire Strikes Back – Harrison Ford Plays It Cool

At the end of the film Star Wars: Episode V – The Empire Strikes Back, we are treated to a heartbreaking scene. Our heroes have been captured, and as Han Solo is slowly lowered into a frozen carbonite machine, we hear Princess Leia abruptly cry out, “I love you!” Ever the bad boy master of cool, Han looks back at her and with two words responds with a simple, “I know.”

The original script called for a much different exchange between the two characters. Originally Leia was meant to say, “I love you. I couldn’t tell you before, but it’s true.” To this, Han was meant to answer, “Just remember that, ‘cause I’ll be back.” Apparently actor Harrison Ford felt that was too out of character for Han, and came up with this line instead, which stuck.

19. Saving Private Ryan – Stories From Home

Towards the end of the film Saving Private Ryan, Matt Damon’s character Ryan is sitting with Captain John Miller (Tom Hanks). As they wait for the impending battle, Ryan decides to pass the time by telling Captain Miller a story about his life before the war.

That story, about Ryan and one of his brothers catching their other brother with a girl in the family barn, was completely ad-libbed on the spot. In Peter Bart’s book The Gross, he describes the story as not particularly funny or interesting to Captain Miller which was, interestingly enough, why it worked between the two characters.

20. Jaws – You’re Gonna Need a Bigger Boat

It was 1975, a time before Indiana Jones and Jurassic Park and all the other movies that would make director Steven Spielberg a household name. While working on his breakout film Jaws, it seemed as though Spielberg and his crew were constantly at odds with the producers, who were described in an interview as being very “stingy.”

Many people working on set would try and goad the producers into putting more money towards the film by saying, “You’re going to need a bigger boat,” every time something would go wrong. The line was so catchy that, during the scene where Brody at last comes face to face with that massive great white shark, actor Roy Scheider decided to ad-lib the inside joke as a line right then and there.

NEXT: These unforgettable and incredibly famous movie moments were completely improvised!

21. Casablanca – Looking At You Kid

Today, the 1942 film Casablanca is widely considered by critics to be one of the best films ever made. But, according to the Chicago Sun Times, at the time it was being filmed, nobody imagined that Casablanca would ever be anything special. The filming was reportedly slightly chaotic: by the time they got to shooting, the script hadn’t even been finished.

As a result of working with an incomplete screenplay, many of the lines we remember from the film were made up on the spot by the remarkably-talented actors. One memorable line was during Humphrey Bogart’s bittersweet farewell to Ingrid Bergman, “Here’s looking at you kid,” which has since hit number five in AFI’s 100 Years…100 Movie Quotes.

22. Good Morning Vietnam – Robin Williams as the Radio Host

According to an interview with Barry Levinson, the director of the 1987 film Good Morning Vietnam, he knew he had a unique opportunity working with actor and comedian Robin Williams. “Robin…is extremely funny and improvisational; and then the thing is, let’s take advantage of those things. ‘Cuz there’s a guy on the radio making up stuff, it’s not like he wrote out everything every morning — he’s making up stuff.”

Levinson goes on to describe filming the scene as being very “loose,” with Williams riffing, making up the dialogue during each take. Afterwards the two men would sit and discuss it, and then they’d do another take. All those moments added up to Williams essentially improvising entire scenes.

23. Crazy, Stupid, Love – Dirty Dancing

On Valentine’s Day 2019, Entertainment Weekly decided to take a look back at the romantic comedy, Crazy, Stupid, Love, and discovered a big secret. Apparently, the Dirty Dancing scene where Jacob (Ryan Gosling) lifts Hannah (Emma Stone) over his head was based on a real event.

While discussing the script, Gosling told a story about how he had done the Dirty Dancing move in real life with someone. Immediately directors Glenn Ficarra and John Requa looked at each other and decided that scene simply had to be in the movie. Reportedly, Gosling was horrified and initially refused. But after some persuasion (and a lot of practice) the lift ended up in the film.

24. 50/50 – Head-Shaving

In the comedic yet tearful film 50/50, Adam, played by Joseph Gordon-Levitt, is suffering from cancer and decides to shave his head while his friend Kyle, played by Seth Rogen, watches encouragingly. According to Rogen, aside from the fact that Gordon-Levitt was shaving his head, no other dialogue or notes had been given. The actors were left to their own devices to make the scene funny.

Rogen explained, “We only had one shot at it. It was the first day of filming, and we improvised the whole thing, which is not wise when it’s something you have one take for, but it turned out funny. It went exactly how you see it.” Guess that means that Kyle’s look of surprise wasn’t entirely acted on Rogen’s part.

25. Goodfellas – You’re a Funny Guy

There’s a particularly tense scene out of many in the 1990 Martin Scorsese gangster movie Goodfellas. Henry Hill (Ray Liotta) and Tommy DeVito (Joe Pesci) get in an uncomfortable exchange Henry’s comment telling DeVito he’s funny turns into DeVito threateningly asking him, “Funny how? Am I a clown? Do I amuse you?”

Apparently, that improvised scene was based on an actual exchange that a young Joe Pesci himself had had with a known gangster while working as a waiter. After hearing the anecdote, Scorsese told Pesci to ad-lib a scene like that, but not to tell anybody else since he wanted to capture the looks of surprise on everybody’s faces in real time.

Sources: Rolling Stone, Business Insider, IMDb