The 20 most famous movie line of all time was made up on the spot.

Filmmaking is a precarious process. A director can begin with a clean slate vision that changes constantly during the filming process. One of the primary instigators of these changes is the actors, who tend to bring spontaneous creativity into their acting. Although improvisations sometimes lead to a director’s hurried “cut,” there are moments when these spontaneous lines perfectly enhance a scene, even the whole film. Following are some of the legendary lines which, by going off-script, turned out to be irresistible cinematic treasures.

‘You Can’t Handle the Truth!’

In the classic courtroom showdown in “A Few Good Men,” Lieutenant Daniel Kaffee (Tom Cruise) insists on truth from Colonel Nathan Jessup (Jack Nicholson). Nicholson was originally supposed to reply with, “You already have the truth!” Instead, Nicholson ad-libbed the now famous retort, “You can’t handle the truth!!” His added pause after the delivery enhanced the statement’s deep impact.

‘She Talks in Her Sleep’

The classic “Indiana Jones” trilogy is famous across the globe, with the next one arguably better than the last. In “Indiana Jones and the Last Crusade,” the crew and cast erupted in laughter when Sean Connery, as Indiana’s dad, delivered an ad-lib one-liner. When Indiana (Harrison Ford) and Henry Jones (Connery) are taken hostage, Indiana asks his father how he knew Elsa (Alison Doody) was a Nazi. Henry matter-of-factly responds, “She talks in her sleep,” provoking a raucous reaction on set. Director Steven Spielberg is said to have shouted, “Well that’s in,” meaning the line would be included in the final cut.

‘I’m Walkin’ Here!’

“Midnight Cowboy” a tale of two con men forming an unlikely alliance, is a cinematic masterpiece, with one of its most memorable moments stemming from an unplanned New York City incident. When a taxi nearly hit Dustin Hoffman and Jon Voight mid-scene, Hoffman, maintaining his character as “Ratso” Rizzo, ad-libbed, “I’m walkin’ here! I’m walkin’ here!” This improvisation was so smoothly executed that it was incorporated into the final film.

‘I Know’

The “Star Wars” universe, with its iconic heroes, villains, and space creatures, has left an indelible imprint on film. In “The Empire Strikes Back,” Harrison Ford, playing Han Solo, improvised a defining reply that is now legendary. Following Leia’s (Carrie Fisher) declaration of love, Han, scripted to share the same feeling, instead responds with, “I know.

‘Hey Malkovich, Think Fast!’

In the award-winning movie “Being John Malkovich,” a chance highway mishap became one of the film’s most iconic moments. A drunken extra throws a can at the head of John Malkovich and shouts, “Hey Malkovich, think fast!” The surprise action and the spontaneous response of Malkovich thrilled director Spike Jonze, who added it to the film. As such, the extra was credited as an actor.

‘I Don’t Care’

Tommy Lee Jones clinched an Academy Award for Best Supporting Actor in “The Fugitive” with an off-script line that captured his character’s essence. In a climactic tunnel chase scene, Dr. Richard Kimble (Harrison Ford) pleads his innocence, to which Jones’ character, U.S. Marshal Samuel Gerard, originally scripted to respond with, “That’s not my problem,” instead retorts, “I don’t care.” The ad-libbed line not only fit the character but also secured an Oscar for Jones.

‘Funny How? I Amuse You?’

In the world of filmmaking, the most memorable moments sometimes come from spontaneous inspiration rather than rigid scripting. This was the case with Martin Scorsese’s mobster masterpiece, Goodfellas, a film brimming with unforgettable lines. Perhaps the most renowned among these is Joe Pesci’s confrontational “Funny how?” Although it wasn’t part of the initial script, Pesci and Ray Liotta had rehearsed this moment off-camera. Impressed by the raw, gripping energy, Scorsese decided to incorporate it into the film.

‘You Talkin’ to Me?’

Taxi Driver, the 1976 classic film, provided one of the most well-known lines in film history, thanks to Robert De Niro’s Travis Bickle: “You talkin’ to me?” Surprisingly, this now-famous line was not scripted. The script only indicated, “Bickle talks back to himself in the mirror.” De Niro used this as a prompt and gave one of his classic improvised monologues.

‘You’re Gonna Need a Bigger Boat’

In Steven Spielberg’s Jaws, Roy Schneider, playing Chief Martin Brody, utters the chilling line, “You’re gonna need a bigger boat” after getting a horrifying glimpse of the monstrous great white shark. The line, an inside joke on the set about the film’s budget constraints, was spontaneously included by Schneider during one take. Its perfect fit into the scene ensured its place in the final cut.

‘I’ll Bet You Could Suck a Golf Ball Through a Garden Hose’

Stanley Kubrick’s Full Metal Jacket is a powerful depiction of the harsh realities of war. The film’s most memorable character, a Marine drill instructor portrayed by R. Lee Ermey, wasn’t scripted. Ermey, who was originally a technical advisor on the production crew, was promoted when Kubrick couldn’t find an actor who could match Ermey’s genuine drill sergeant attitude. Most of Ermey’s lines were ad-libbed, giving his character an authenticity unmatched by any other actor.

‘Take the Cannoli’

The Godfather, one of the all-time great motion pictures, also contains an immortal improvised line. In a key sequence, Peter Clemenza (Richard Castellano) tells a henchman to “Leave the gun.” The line was written, but Castellano improvised “Take the cannoli.” The showbiz surprise resonated with director Francis Ford Coppola, who chose to leave the line in the finished film.

Hannibal Lecter’s Hissing Sound

In the Oscar-winning The Silence of the Lambs, Hannibal Lecter, played by Anthony Hopkins, controls each scene he appears in, even though he’s only on screen for 25 minutes of the 120-minute movie. His chilling statement, “I ate his liver with some fava beans and a nice Chianti,” followed by a menacing hissing noise, has become synonymous with the character. The ominous sound was a spontaneous inclusion by Hopkins, which rendered his co-star, Jodie Foster, speechless during the scene. It was this unpracticed, spontaneous reaction that earned Hopkins an Academy Award for Best Actor.

He Stole My Line’

Good Will Hunting, the movie that catapulted Matt Damon and Ben Affleck to fame, is dotted with a stand-out line given by Robin Williams. Williams, who is acting as Dr. Sean Maguire, shares the anecdote of how he met his wife, celebrating the moment with the line, “Sorry guys, I gotta see about a girl.” Towards the end, Damon’s character, Will Hunting, reuses the same line to leave for California. Williams should have been kept quiet while the line is being played back in a voiceover, but he naturally responds with, “Son of a b*tch. He stole my line.” That natural moment of authentic humor was too good to be omitted.

‘People Call Me Forrest Gump’

Forrest Gump, the heartwarming classic, provided us with unforgettable friendship of Forrest and Benjamin Buford Blue, known as Bubba. Tom Hanks’ written line was simply to state his introduction as Forrest Gump, but Hanks opted for imitating Bubba’s introduction by stating, “People call me Forrest Gump.” This little touch brought a nice bit of endearing naivety to the character that Robert Zemeckis, the director, chose to retain.

‘Like Tears in Rain’

In the climactic moment of the sci-fi classic Blade Runner, Rick Deckard, Harrison Ford, is rescued by the dying replicant, Roy Batty. The original script had a long soliloquy for Batty, but actor Rutger Hauer spontaneously cut it short on the day of filming, adding the now-famous line, “All those moments will be lost in time, like tears in rain.” This spontaneous cut lent a brief yet powerful insight into the replicant’s human-like existence, resulting in what is now hailed as one of the greatest lines of science fiction films. The last line is: “I’ve seen things you people wouldn’t believe. Attack ships on fire off the shoulder of Orion. I watched C-beams glitter in the dark near the Tannhäuser Gate. All those moments will be lost in time, like tears in rain. Time to die.”

‘Want to Hear the Most Annoying Sound in the World?’

Prior to his blockbuster film successes, Jim Carrey was a highly popular comedian with a keen sense of humor and ad-libbing talent on the sketch comedy program In Living Color. His improv talents were skillfully showcased in Dumb and Dumber, especially in the unforgettable scene wherein Harry (Jeff Daniels) and Lloyd (Carrey) give a ride to a hitman when they’re hitchhiking. The whole scene, from Lloyd’s notorious “most annoying sound in the world” and their performance of “Mockingbird,” was improvised, the director said.

‘I’m King of the World!’

In the epic love drama Titanic, perhaps the most famous line of dialogue from the movie was completely ad-libbed. The triumphant declaration by Leonardo DiCaprio that he’s the “king of the world” was not in the original script. In fact, DiCaprio initially yelled the line out of spontaneous reaction when he first walked aboard the ship before shooting. Director James Cameron was so enamored with the line, he demanded its inclusion in the script to inject a bit of light-hearted merriment into the love scene.

‘Here’s Lookin’ at You, Kid.’

The classic film Casablanca has yielded some of the most recognized lines of all time. Its most popular line, however, would never have gained public awareness if actors stuck to the script. The famous line was indeed heard offstage, as Humphrey Bogart uttered it to Ingrid Bergman while instructing her in poker during a break in shooting. In a reference to the line from Titanic, it was included in the script because of its remarkable play on words

‘I’m Singing in the Rain.’

Stanley Kubrick’s A Clockwork Orange, infamous for its dread-inducing ultraviolence and dystopian landscapes, transformed a classic show tune into an uncanny dread song. Unbeknownst to many, this iconic scene was not part of the original script. When Malcolm McDowell improvised a song during the home invasion scene, Kubrick was so impressed by the ad-lib that he decided to include it in the film.

‘Mein Fuhrer, I Can Walk!’

Dr. Strangelove, a movie which satirizes military existence as well as denounces war, has Peter Sellers playing the iconic role of the dotty scientist, Dr. Strangelove. The film is full of ad-libbed lines, the most iconic of which is an impromptu addition by Sellers. The line, spoken at the end by the Nazi physician, was improvised by Sellers on the spot and has now become synonymous with the movie.