Clockwork's Classical Conditioning

In the film A Clockwork Orange, classical conditioning is used to produce a negative effect every time Alex is exposed to violence. Previously an abnormally violent young man, Alex was had been in jail at the time he was chosen for this experimental treatment. The stimuli the doctors expose Alex to are violent video clips. While he watches these clips, doctors drop an unknown drug into Alex's eyes, which causes him to feel extremely sick. This sick feeling is the conditioned response to the violent video clips. He inadvertently conditioned to feel sick anytime he heard Beethoven's 9th, which happened to be his favorite piece of classical music. This accidental conditioning is so important to the film that the soundtrack to the movie features Beethoven rather than Alex.