The Joker’s Slow Clap: It was Heath Ledger’s stroke of genius that created the Joker’s slow clap in The Dark Knight, in response to Jim Gordon’s victory speech. This helped Health develop the Joker’s character into an unpredictable villain rather than the classic, predictably evil character.

“You talking to me?” from Taxi Driver: It’s clear that Robert De Niro had a great time exploring his character. So much so that he improvised the entire scene where he’s talking to himself in the mirror, and produced one of the most recognizable lines ever.

Dumb and Dumber’s most annoying sound in the world: Not only were Jim Carrey’s annoying road trip antics unscripted, but so was Jeff Daniel’s hysterical laughter. Even the hissy fit by hit man Joe Mentalino was unplanned.

Don Corleone’s cat-stroking in The Godfather: Marlon Brando is widely heralded as one of the greatest improvisers in the business. A stray cat was found wandering around on set and Brando came up with the idea to gently stroke the cat on his lap while ordering mob violence, a scene that has been recreated many times since and helped set The Godfather up as a classic.

“Here’s Johnny!” in The Shining: As if Jack Nicholson tormenting his wife and child with an ax wasn’t enough, he then decided to ad-lib an over-the-top impression of Ed McMahon with the infamous head-through-the-splintered-door line.

That sneeze in Annie Hall: Woody Allen’s 1977 Best Picture-winner “Annie Hall” was charming and hilarious. Albie’s sneeze during the coke scene was completely unplanned, and added an element of slapstick comedy that viewers loved.

That Fake Orgasm in When Harry Met Sally: The diner scene with the over-the-top orgasm was all Meg Ryan’s idea, and it coined the classic line, “I’ll have what she’s having”.

The necklace box snap in Pretty Women: What started as merely a practical joke between Richard Gere and Julia Roberts became one of the best scenes in the movie. The director loved Roberts’ genuine laughter and wisely left the scene in.

The Hsssssss in Silence of the Lambs: Hannibal Lector’s speech was all written, but we can thank Anthony Hopkins for the terrifying hssssss sound.

Han Solo’s response to “I love you” in The Empire Strikes Back: Han Solo’s classic line “I know,” in response to Leia’s declaration of love was all Harrison Ford. The scripted line was “I love you too,” but Ford thought that wasn’t very Han. George Lucas was against it at first, but it’s now gone down in history as one of the great Star Wars moments.

Robin William’s farting wife in Good Will Hunting: Amazingly, the scene where Robin William’s character tells Will about his late wife farting in her sleep was completely improvised on the spot. The shows that comedians make the best ad-libbers, and Williams was one of the best.

“I Don’t Care” in The Fugitive: The showdown between Kimble (Harrison Ford), accused of murdering his wife, and Gerard (Tommy Lee Jones) produced one of the greatest ad-lib lines in movie history. Kimble pleads “I didn’t kill my wife,” to which Tommy Lee Jones, unscripted, replied “I don’t care.” This line reinforced that Gerard was out to get Kimble, no matter what.

Peter Sellers in Dr Strangelove: In terms of slapstick comedians, Peter Sellers was in a league of his own. His improvised line, “Mein Fuhrer! I can walk!” It became one of the most iconic lines in the movie.

Singing in the Rain in A Clockwork Orange: Malcolm McDowell, like any actor, must have struggled with the though of playing a psychotic rapist. Director Stanley Kubrick demanded this scene to be re-shot many different times, and McDowell reacted by belting out “Singing In The Rain” during this harsh act of violence.

John Malkovich hit by a can in Being John Malkovich: Rather than a pre-planned scripted action, the can that hit John Malkovich was thrown by a drunk extra. Director Spike Jonze left it in because it showed Malkovich’s vulnerability and frustration.

“Why male models?” from Zoolander: The first time Ben Stiller asked “Why male models?” it’s completely scripted. Hand Model J.P. Prewitt provides a lengthy explain as to why, during which Stiller forgot his next line, causing him to repeat his last line “why male models?” David Duchovny, playing Prewitt, then ad-libbed “Are you serious? I just told you that a moment ago.” This resulted in a hilarious scene that reinforces the utter stupidity of Stiller’s character.