It's easy to forget how many elements of movies come from unexpected places.

Steven Spielberg came up with some of Jaws' most inventive scenes because his crew couldn't get the mechanical shark to work. Viggo Mortensen's famous scream in The Two Towers happened because he'd just broken his toe by kicking a prop helmet. And the guy who threw the orange at Sylvester Stallone during Rocky's jogging sequence was a random Philadelphian who didn't seem to know a movie was being filmed.

But a particularly fascinating example occurred in 1981, centered on the television premiere of Halloween. Within, John Carpenter helped cement — against his better judgment — the franchise's greatest controversy.

Originally released in 1978, Halloween is one of the most influential horror movies ever made. Its astounding financial success — earning $47 million on a budget of $325,000 — helped launch the '80s slasher film craze, and Carpenter's filmmaking chops inspired countless imitators. By 1981, a sequel, Halloween II was in the works, and the original was already a legend in the horror world. Unfortunately, because VHS and Betamax machines and rentals were still relatively rare (the first movie rental store in America had only opened in 1977), it could be difficult to see the film if you hadn't caught it in theaters.

Consequently, NBC decided to give the film its TV debut on Friday, Oct. 30, the same night the sequel was set to debut in theaters. It was a great idea for a cross-promotion; hopefully home viewers would be inspired to watch the sequel in theaters. But there was a problem: The original Halloween clocked in at a tight 91 minutes, which was too short for the NBC time slot, even allowing for commercial breaks.

So Carpenter was forced to shoot several extra scenes to pad the material (in addition to slightly re-editing the film to take out some swearing and drug use).

Most of these additions are fairly innocuous. One, which takes place when Michael Myers is still a kid, shows his doctor Sam Loomis (Donald Pleasence) arguing to a two-person medical board that Michael should be moved to a higher-security facility. After this, Loomis visits Michael in his cell, where his deadly young patient sits motionless in a chair, staring out the window. "You've fooled them, haven't you?" Loomis tells him, certain that Michael's comatose behavior is an act. "But not me."

But the most important addition comes after Michael, now grown, has broken out of the mental hospital and is on his way back to his home town of Haddonfield, Ill., to terrorize Laurie Strode (Jamie Lee Curtis). Loomis visits the cell Michael escaped from, finding the word "sister" scrawled on the door.

As these additional sequences were being planned and shot, Carpenter and co-writer/co-producer Debra Hill were also involved in the writing and production of the sequel. It seems like neither the extended material of the first movie nor the sequel itself had a ton of appeal for Carpenter, but he took them on because, as he said in a 1984 interview, "There are two sides to when you work in the movie business. One is as an artist…the other side is the business person."

Writing and producing one film while reshooting another was a grueling process, and at some point Carpenter made the fateful choice to turn Myers and Strode into siblings. "I didn't have anything to add," he said in a 2019 interview. "So I came up with this brother thing. It was awful, just awful. But I did it."

This revelation became one of the surprise twists of Halloween II. And with the new footage in the TV airing of the first film, Carpenter had retconned it into the original as well. It was a decision that would forever shape the franchise and in the process launch a thousand controversies.

The idea that Michael and Laurie were brother and sister became a cornerstone of the Halloween movies. In the late '80s and '90s, three sequels (Halloween 4, 5 and 6) took the premise as far as they could, trying to develop it into a full mythology; later films played it up or down, depending on their direction. But it was never a universally loved idea. For decades, fans argued about whether it was a departure from the original film's conceit — and whether it was even a good concept in the first place.

By the time of the most recent reboot, dissatisfaction with the trope had grown so strong that the decision was made to retcon the entire franchise...yet again. The 2018 Halloween basically declared that every other sequel hadn't really happened, that the footage in the 1981 TV airing was a mistake and that the idea that Michael and Laurie were related was preposterous. We're now back to the original 1978 idea of an unknowable murderer trying to kill an unrelated woman for incomprehensible reasons.

Will this state of affairs last? Or will the sibling plotline get resurrected somewhere down the road? Who knows. But one thing's certain: If Michael and Laurie do end up as brother and sister again, it will probably have to do with a lot of things not necessarily related to good storytelling.

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