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 Backlash: The film was the subject of much media hype linking it to violent crimes. After Stanley Kubrick received death threats, 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. Malcolm McDowell developed a lasting hatred for eye-drops from filming this scene.
Throw It In: 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. Additionally, near the end, the man feeding Alex while Alex mocks him about it by 'popping' his mouth open while the man spoke to him came about as a result of Kubrick being in a particularly bad mood and McDowell acting goofy in an attempt to cheer him up. Considering it was used in the film, it's probably safe to say it worked.