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It's now been 40 years since "Alien" hit theaters and kicked off one of the most popular sci-fi movie franchises of all time. From the unexpected downsides of the Xenomorph costume to the Hollywood stars who almost appeared in the movie, here are 15 things you might not have known about the making of "Alien."

1. The original screenplay featured the title "Star Beast," but writer Dan O'Bannon decided "Alien" was more effective and direct.

2. Harrison Ford was originally offered the role of Captain Dallas but turned  down the part.

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3. According to director Ridley Scott, Meryl Streep was also strongly considered for the role of Ripley and may well have been cast if not for the sudden death of her partner, John Cazale.

4. Jon Finch was originally cast as Kane, but had to drop out on the first day of filming due to complications from diabetes.

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5.H.R. Giger's original Xenomorph design included visible eyes, but this was removed in order to give the creature a more inhuman appearance. Scott also purposely avoided filming the Xenomorph straight-on, in order to emphasize its terrifying nature.

6. In order to create the set for the Xenomorph egg chamber, the crew borrowed a set of laser lights from The Who, who were rehearsing on a nearby sound stage.

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7. The facehugger was originally meant to be painted green, but O'Bannon liked the stark, humanoid look of the unpainted puppet and chose to leave it as-is.

8. Many of the gore effects were achieved by using raw animal parts, including cattle hearts and sheep intestines. That helped fuel the actors' genuine reaction of fear during the infamous chestburster scene.

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9. The names for the Nostromo crew members were chosen in part because they're gender-neutral. None of the characters have a specified gender in the screenplay.

10. The crew had to design a special swing for actor Bolaji Badejo because his Xenomorph costume made it impossible to sit down in between takes.

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11. One of the early shots of the interior of the Nostromo features a coffee grinder hanging on a wall. That prop was later used to create the Mr. Fusion engine in "Back to the Future."

12. Most of the creatures models had to be repainted every single day due to the corrosive effects of the slime used to coat them.

13. The Space Jockey prop measured a full 26 feet tall. Unfortunately, it was accidentally destroyed when a discarded cigarette set it on fire.

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14. One of the many deleted scenes from "Alien" features Ripley and Dallas having casual sex as a way of relieving the boredom of their journey. Scott eventually re-purposed that idea for 2012's "Prometheus."

15. The Xenomorph only appears on-screen for a total of four minutes in the theatrical cut.