Here are five great unscripted scenes that our movie memories couldn't do without.

1. Beginning a beautiful friendship

Perhaps no movie has as many famous one-liners as Casablanca (1942). But they weren't all the work of screenwriters Julius J Epstein, Philip G Epstein and Howard Koch (who deservedly won an Oscar for their work). Based on Murray Burnett and Joan Allison's unproduced play Everybody Goes to Rick's, the script was written in a hurry, and was still going through rewrites when filming commenced. As a result, some of the best lines were improvised. "Here's looking at you, kid," Humphrey Bogart's farewell line to Ingrid Bergman, was a popular quote in the 1930s. Bogart ad-libbed it while filming Casablanca, and it worked so well that was used twice. In 2007, Premiere magazine named it the best greatest-ever movie line. Bogart's final line, however, was created just for the film. Who can forget that last shot, as Rick (Bogart) and Captain Louis Renault (Claude Rains) walk away, planning to escape Casablanca after assisting in a noble cause. "Louis, I think this is the beginning of a beautiful friendship," says Rick. The line was created by producer Hal B. Wallis, and dubbed by Bogart after filming was completed.

2. Indy vs. the Swordsman

In one of the coolest and most memorable scenes of Raiders of the Lost Ark (1981), Indiana Jones (Harrison Ford), ready for action, is confronted by an evil-looking swordsman. Rather than engage him in hand-to hand combat, he gives the swordsman a tired, "you must be joking" expression, pulls out his gun and casually shoots him. This funny and clever moment, filmed in Tunisia, might never have happened if Ford and most of the crew weren't suffering from food poisoning. Initially, Indy was supposed to defeat the swordsman in an extended fight sequence, using his famous whip. However, as he was so ill, the scene just wasn't working. Instead, director Steven Spielberg allowed him to dispose of his foe in this simpler, but no less effective method. The tired look on Indy's face, of course, was utterly real.

3. "You ain't heard nothing yet!"

Warner Brothers' The Jazz Singer, immortalized as the first-ever talking picture, was basically a silent film, with just a few moments of synchronised sound. The audio was mainly just a few opportunities for the star, Al Jolson, to sing hit songs like My Mammy and Blue Skies (later a hit for Willie Nelson). The small amount of dialogue was ad-libbed by Jolson and Eugenie Besserer (who played his mother "“ or his "mammy"). Jolson spoke a grand total of 281 words in the film, and the most memorable line was his final one: "Wait a minute, wait a minute. You ain't heard nothing yet!" It was a prophetic quote, and more than 70 years later, it would earn a place in the American Film Institute's list of the greatest movie lines. Because Jolson's line was so off-the-cuff, it might have been removed from the final cut if Sam Warner, the driving force behind talking pictures, had not insisted that it stay. Sadly, Warner died of a sinus infection a day before the film's release, meaning that he would never witness it making history.

4. The Odessa Steps Massacre

One of the most famous and powerful scenes in movie history, still harrowing after 84 years, showed Tsarist troops slaughtering Russian civilians at the port of Odessa during an unsuccessful 1905 revolution. It was part of Bronenosets Potemkin (1925), known to English-speakers as Battleship Potemkin (or simply Potemkin), commissioned by the Bolskevik authorities to a young filmmaker, Sergei Eisenstein, to fill the public with revolutionary zeal. The sequence originally it took up only three pages of a huge screenplay called The Year 1905 by Nina Agadzhavana-Shutko, a veteran of the 1905 revolution. It was conceived as an eight-part epic, with action taking place at locations around the Soviet Union, but the shooting was interrupted by bad weather (it was winter), making it impossible to meet the deadline. While in Odessa, however, Eisenstein decided to focus on one incident: the mutiny by sailors, and the subsequent massacre of civilians who supported them on the steps at Odessa. To increase the power of the scene, Eisenstein invented "montage", editing numerous images in a vigorous and dynamic way. Soldiers inhumanly mow down the civilians; people are shot through the head (in close-up); crowds panic, trampling each other; and (most suspensefully) a mother loses control of her baby's pram, which bounces down the steps before eventually overturning. It's one of the most influential, imitated (most famously in The Godfather and The Untouchables) movie scenes, but it might have never happened if the weather had been better.

5. The Dance of Death

Ingmar Bergman's 1957 masterpiece Det Sjunde Inseglet (The Seventh Seal) is set in medieval Sweden, ravaged by the black plague, where a knight returning from the Crusades (Max von Sydow) challenges Death (Bengt Ekerot) to a game of chess. Inevitably, the knight loses in the end. In one of the final scenes, he and five other characters are led away by Death, in the eerie "Dance of Death" sequence, shot against an ominous, cloudy background as the sun prepares to set. This very famous moment wasn't in Bergman's original script (or in his play, on which it was based), but added at the end of the day's filming, when he noticed the visual effect of the clouds. Showing the doomed "dancers" in silhouette makes for a powerful image, but it was also a practical one. Most of the actors had already gone home, so Bergman arranged some technicians and nearby tourists to throw on the costumes as stand-ins. To the tourists, this must have been a real buzz. Spontaneously appearing in a movie is cool, but appearing in one of the greatest scenes of movie history must have been an incredible thrill.