Sometimes, the genius moments of a film weren't in the script, and happened in an off-the-cuff moment on the shoot itself. Here are 10 examples of when an ad-lib or off-script moment went very, very right...

Taxi Driver: "You talkin' to me?"
(Martin Scorsese, 1976)

Arguably the most famous cinematic quote of all time, "You talkin' to me?" was actually improvised. Even though the film's screenplay was written by the brilliant Paul Schrader (who also wrote the adapted screenplay for Scorsese's Raging Bull), it's this line which has gone down in the annals of pop culture history.

Director Martin Scorsese has always encouraged Robert De Niro's creativity, proving that actors can contribute more than just their performance, and in this instance it paid off.

In the original script Schrader had simply written "Bickle speaks to himself in the mirror." Alone in his grubby apartment, De Niro's loner sociopath character Travis Bickle is planning to shoot a politician. In the mirror he is practising with the sleeve-holster he made for his gun. Catching his reflection, he postures, repeating "You talkin' to me?" before whipping out his gun and taking aim. It is a moment of stunning personal insight into a character as flawed, intriguing and complex as you will ever see on the big screen.

The Shining "Heeeeeere's Johnny!"
(Stanley Kubrick, 1980)

Adapted from the Stephen King novel of the same name, The Shining is one of Kubrick's best known and most commercially successful films. The shoot was a famously difficult one, as Kubrick was notorious for being a controlling, sometimes cruel, filmmaker.

It's common knowledge that the fear displayed by Shelley Duval (playing Wendy Torrance) in the film was genuine. Kubrick would scream and shout at her, and allegedly even slapped her across the face during one take. So the spooky, tense and horrifying atmosphere we see on screen is often authentic, and perhaps inspired Jack Nicholson to ad-lib one of his most famous lines.

Jack Torrance (Nicholson's character) slowly loses his mind when stationed to mind a remote hotel with his wife and little boy. At a pinnacle stage in the narrative, he chases his wife (Duval) through the hotel with an axe. She locks herself in a bathroom, and when Torrance chops through the door, he pokes his demented face through the hole and wails, "Heeeeeere's Johnny!"

Nicholson was mimicking the catchphrase used by Ed McMahon to introduce Johnny Carson on The Johnny Carson Show (a hugely popular show at the time). It is this juxtaposition, in terms of connotation and context, that gives it such a magnificently dark, creepy, yet disturbingly humorous, effect.

Despite the screenplay being adapted from a book by one of the best horror novelists of all time, "Heeeeeere's Johnny!" is certainly the most easily remembered line from this uber-stylish classic.

Indiana Jones And The Raiders Of The Lost Ark: Jones shoots the swordsman
(Steven Spielberg, 1981)

The story behind this scene is almost as famous as the scene itself. Harrison Ford, playing our protagonist explorer Indie Jones, got a bad case of food poisoning and dysentery. He was due to shoot a big fight scene with a skilled swordsman the next day. Not able to take on the action, Ford suggested to Spielberg that he simply shoot the over-zealous antagonist, in a quip that sums up the ethos and feel of Jones' character perfectly.

So, following an arduous journey through the streets of Egypt, the crowd parts to reveal a sinister, threatening swordsman dressed in black. He faces Jones, but straight after he cuts some impressive pre-fight moves in an attempt to intimidate his opponent, Jones draws and shoots him down in one. And off-script movie magic is made.

Blade Runner: Roy Batty's final soliloquy
(Ridley Scott, 1982)

With Harrison Ford in the lead again (this time as Rick Deckard) we come to Ridley Scott's revered sci-fi epic Blade Runner. The screenplay was based on the Philip K. Dick novel Do Androids Dream Of Electric Sheep?.

Hollywood legend has it that Martin Scorsese was originally interested in the adaptation but never optioned it. That would have been interesting. But we all love Scott's dark, moody, original and highly influential shoot which launched a thousand mimics. And we especially love the Aryan, cold, violent Roy Batty, the perfect replicant (android).

Played fantastically by Rutger Hauer, Batty is LAPD Officer Deckard's nemesis. In the end Batty's life is drawing to a close, and like so much in the film, it makes a social comment on all kinds of issues.

So, sitting on a rooftop in the pouring rain Hauer takes the first few lines from David Peoples' script and adds a couple of very memorable closing lines as his character's last words. "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 Tannhauser gate. All those moments will be lost in time. Like tears in the rain. Time to die."

Mad to think Bladerunner is set in 2019. Doubt we'll have such perfect androids in only ten years' time.

The Third Man: Lime's cuckoo clock maxim
(Carol Reed, 1949)

Carol Reed's The Third Man is a film that constantly appears on 'best film' lists. It's a beautifully shot and scripted testament to the art of film noir, starring notorious movie heavyweight Orson Welles. It also has one of the most ferociously famous theme tunes in film history (even if it doesn't come to mind right now, you do know it).

One of its most memorable moments comes when Harry Lime (Welles) is trying to convince his old friend Holly Martins (Joseph Cotton) to join him in some dubious dealings. He's explaining that to make omelettes you need to break eggs.

Illustrating Welles' absolute cinematic brilliance, he includes the cuckoo line. It was not part of the original screenplay, adapted from a novel by reputable writer Graham Greene, but is perhaps the best known quote of the film: "In Italy for 30 years under the Borgias, they had warfare, terror, murder, bloodshed. They produced Michelangelo, Leonardo da Vinci, and the Renaissance. In Switzerland they had brotherly love, five hundred years of democracy and peace. And what did that produce? The cuckoo clock."

Midnight Cowboy: "I'm walkin' here!"
(John Schlesinger, 1969)

Okay, it's been disputed as to whether this was off-script or not. But it's not past the methodical Dustin Hoffman to ad-lib such a brilliant line.

Midnight Cowboy won Academy Awards for Best Picture, Best Director (John Schlesinger) and Best Adapted Screenplay (Waldo Salt). It's the only X-rated film to have won any Oscars, and the only other X-rated nomination in history was Kubrick's A Clockwork Orange (1971).

There is a scene in which Hoffman's unforgettable 'Ratso' Rizzo is walking our midnight cowboy Joe Buck (played by a young Jon Voight) through the streets of New York. He's coaching him about becoming a successful stud and gigolo, and while crossing a street nearly gets hit by a yellow cab. Hoffman beats the hood with his fist and shouts, "I'm walkin' here!" in his unique New York parlance, yhen quickly retorts to Voight, "Actually, that ain't a bad way to pick up insurance y'know."

"I'm walkin' here." is often cited as one of the world's best movie quotes. It's usually thought of as an improvised line, which Hoffman has claimed. And he is certainly more than capable of this kind of fleshed-out character portrayal. But producer Jermoe Hellman has always maintained that it was in the script. The romantic film buff in me likes to believe the former, but I guess we may never really know.

Dr. Strangelove, Or: How I Learned To Stop Worrying And Love The Bomb: Dr. Strangelove's sporadic involuntary Nazi salute
(Stanley Kubrick, 1964)

Apparently, so many of Sellers' lines in Dr. Strangelove were improvised that he is often cited as an uncredited co-writer. And it is considered a study of retro-scripting, ie. when ad-libbed lines are later written into the final script. So, it's difficult to know which one to pick, but perhaps the most ingenious and intuitive is when his title character performs sudden involuntary Nazi salutes in the company of the US military (Sellers plays three characters in total).

Dr. Strangelove is a wheelchair-bound German nuclear weapons expert, who has a past association with the Nazis. In one of the best comedic performances of all time, Sellers' Dr. Strangelove sometimes accidentally refers to the US President as 'Mein Fuhrer', and strangles himself with his out-of-control right arm. This is as well as having to use his left arm to push down the Nazi salutes his right arm frequently and uncontrollably lapses into.

This was entirely Sellers' creation. So much so, in fact, that the novel from which the film was adapted (Red Alert by Peter George) didn't even have the character Dr. Strangelove at all. The word genius does get thrown around but, good lord, Peter Sellers really deserves the moniker.

Goodfellas: "Funny how?"
(Martin Scorsese, 1990)

Adapted from the Nicholas Pileggi book Wiseguys, the Goodfellas screenplay is not without its share of memorable moments. It is one of the best loved films of all time, and displays a darkly humorous side to the Italio-American gangster genre, largely absent in Coppola's The Godfather series.

People always remember the crazy Joe Pesci character, Tommy DeVito, who defined and inspired a million mafia-esque archetypes. Such is the unstable and changeable world of mafia relationships that in one scene DeVito is sitting with our protagonist Henry Hill (Ray Liotta), sharing a drink and having a laugh. When Hill comments, "You're a funny guy," DeVito's face turns stone cold and he replies, "What do you mean I'm a funny guy. Funny how? Funny like I'm here to amuse you?'" The entire room stops dead. A couple of wiseguys mumble, "Hey, Tommy, calm down," as Hill looks worried and tries to explain himself.

The tension is just about to turn into what we think will be bullets, when DeVito cracks and says, "I'm just fucking with you," and everyone laughs. With relief, might I add.

It exemplifies beautifully how crazy Pesci's character is. His friends believe he may turn that easily, and also how volatile and suddenly hostile their world can be. It's thought that Pesci ad-libbed quite a lot for this role and that lines such as this were often retro-scripted into the final draft of the screenplay.

Silence Of The Lambs: Hannibal's hissing
(Johnathan Demme, 1992)

Playing one of the most iconic cinema villains ever, Sir Anthony Hopkins immortalised the cannibalistic Dr. Hannibal Lecter in this classic performance. Although he only has under twenty-five minutes of screen time, Hopkins won an Oscar for Best Actor. Jodie Foster also won for Best Actress, and the film won Best Director, Best Screenplay (Ted Tally) and Best Picture too. Not bad.

The American Film Institute named Lecter the number three screen villain ever in their top 100 in 2003, next to Norman Bates, with Darth Vader in the top spot.

Lecter is an incarcerated serial killer cannibal whom Foster's character, FBI agent Clarice Starling, interviews to help find another murdering cannibal, still at large. All in a day's work.

At one point Lecter tells of an unsavoury incident, describing a now-famous meal: "A census taker once tried to test me. I ate his liver with some fava beans and a nice Chianti." He then hisses and sucks at Starling in a truly revolting and disturbing manner, forever putting an entire generation off that particular varietal of wine.

Hollywood rumour says that this hissing was just a joke thrown in by Hopkins. He never intended it to be so frightening, not to mention appearing in the final cut and becoming so utterly conspicuous.

Casablanca: "Here's looking at you, kid."
(Michael Curtiz, 1942)

Ah, Casablanca. What can we say? If it's not your favourite oldie, and the final scene doesn't make you cry, then I'm sure you don't have a reflection in a mirror. But more than the emotion of the story, the coolness of Bogie and the beauty of Ingrid Bergman, it is a technically superb and incredibly entertaining film.

Regarding the script, the famous line, "Play it again, Sam", is not actually in the film and is probably the world's biggest cinematic misquote. Then, to our ad-libbed moment.

During the last scene and their final interaction, Rick (Humphrey Bogart) is doing the right thing and letting Ilsa (Bergman) go. Crying, she tries to convince him to let her stay. He refuses but consoles her, saying, "Here's looking at you, kid." And there isn't a dry eye in the house.

The American Film Institute often calls it one of the most memorable lines in film. It is often quoted and parodied. Yet, legend has it that this is something Bogart used to say to Bergman as he taught her to play poker in between takes on set. It was never in the original script at all.

Special Mention

Mike Leigh and Christopher Guest: nurturing improvisation in film

These two filmmakers cultivate such a culture of improv on their sets that we couldn't quite pick one line or two...

Leigh, known for his gritty, realist portrayals of life in modern Britain, gets his actors to improvise extensively throughout rehearsals. Then Leigh takes what has materialised in this process and goes off to work on the script from there, rather than the other way around. He's won Academy Awards for screenplays by dong this. And it shows, as his work is some of the most interesting and authentic in cinema today. Notable movies include Naked, Happy Go Lucky, Vera Drake and Secrets & Lies.

Christopher Guest works his movie scripts much like Larry David does for Curb Your Enthusiasm. Guest gives the cast a loose outline of the plot and lets his actors work around that, filming the results. Stellar comedic performances by strong actors have produced some of the most famous and original comedies ever, including This Is Spinal Tap and Best In Show.

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