Creator Backlash: In an introduction to a later edition of the book, the author called it "pornographic" and an "embarrassment." He considers its main entertainment value to be from "raping and ripping."
Creator Breakdown: Burgess was paranoid that he was dying of a brain tumor, so he cranked it out in less than a month.
Executive Meddling: In a reversal of the "Hollywood Ending" stereotype, American publishers insisted that the last chapter (where Alex decides to stop being a criminal and raise a family) be removed to make the novel more depressing.
Accidentally Accurate: While mini-cassettes never took off as a music medium, the music store Alex visits almost seems to have anticipated the return of vinyl records some 40 years later. Ditto for Alex's apartment, now that elements of 1970's decor have found their way back into style as well.
Actor-Inspired Element: When Malcolm McDowell, a cricket fan, came in for a costume fitting with his gear, including protective cup, Stanley Kubrick told him to keep them out and incorporate his white shirt and cup into the costume. When Mc Dowell started to dress by putting the jockstrap under his pants, Kubrick told him it would look better over his trousers instead, and the look made it into the final movie.
Approval of God: Inverted; Gene Kelly reportedly did not like the film's take on "Singin' on the Rain" so much that when he met Malcolm McDowell at a party some years later, Kelly turned and walked away in disgust, but mostly because Stanley Kubrick went cheap, didn't keep his word and never actually payed Kelly for the song.
Creator Backlash: The film was the subject of much media hype linking it to violent crimes. After Stanley Kubrick received death threats, along with hearing of the news of two copycat crimes involving the rape of a Dutch girl in the hands of men singing "Singin' in the Rain" and the beating of a 16 year old boy who, while dressed as Alex, beat another boy, he withdrew the film from screening in the UK, even suing arthouse theatres that tried to show it. The ban was only lifted after Kubrick's death.
Dawson Casting: Malcolm McDowell was 27 during filming. Though Alex's age is never given, he's still supposed to be attending school in the beginning of the film. According to the DVD Commentary, Michael Tarn, who played Pete, was the only actor of the four Droogs who was still a teenager, being 19 at the time of filming.
Enforced Method Acting: Malcolm McDowell had actually scratched his cornea during filming, and thus the man with the eye drops during the Ludovico Technique was an actual medical practitioner. Mc Dowell developed a lasting hatred for eye-drops from filming this scene. Years later, he had to get surgery on his eyes because the retinas were detaching. He believes the two events are related.
M.M.: No way. I'm an actor, damn it. This is torture, this is medieval torture! Then the doctor came up and said there will be no hurt. Liar! ...Then they anesthetized my eye. They had all the latest techniques, they poked the corner of my eye with a handkerchief.
Fatal Method Acting: Averted. It is often claimed that Malcolm McDowell nearly drowned when his breathing apparatus failed during filming of the waterboarding scene. This is not true. Daily records indicate that the scene was filmed in repeated takes with no stoppage from equipment failure. Mc Dowell has never reported a near drowning, while he does report many similar close calls in other scenes.
Missing Trailer Scene: The trailer contains a scene where Basil the snake leaves Alex's room. This doesn't happen in the film.
Retroactive Recognition: Julian, Mr Alexander's nurse/protection, is played by a young weightlifter and wrestler named David Prowse. After seeing the movie, George Lucas was so impressed with his size that he offered him the part of Darth Vader.
Technology Marches On: Alex scams his way into the couple's house by telling her there was a car accident and he needs to use the phone. Nowadays it's 99% certain he would have had a mobile.
Micro Compact Cassettes are used by Alex. Nowadays, it would be either a CD or just part of an iPod playlist.
The scene with Alex dancing while he sings "Singing In The Rain" was the result of Stanley Kubrick finding the scene too conventional and asking actor Malcolm McDowell to improvise. Interestingly, Kubrick only told McDowell to try dancing, not singing. McDowell did, then spontaneously started singing the song. Kubrick liked it so much that, as soon as the take was over, he immediately left the set to secure the rights to the song.
The scene in which Alex "pops" his mouth open for the minister to feed him is entirely improvised, as Kubrick got incredibly bored filming the scene; Malcolm McDowell then started acting silly to keep the crew's attention focused. Considering it was used in the film, it's probably safe to say it worked.
What Could Have Been: Different people wanted to adapt the book before Kubrick. This included one version featuring Alex and his droogs as wealthy old men and another version that would have been used as a vehicle for The Rolling Stones.