There are few horror movies that are as stomach-churning and commercially successful as the films that makeup the Saw franchise. There have been seven films in the torture porn series to date, and the first film is celebrating its very bloody ten-year anniversary this week. The film that started out as an idea for a low-budget horror movie in the vein of The Blair Witch Project, by director Jame Wan and screenwriter Leigh Whannell, would go on to become one of the most successful horror franchises of the last decade, pulling in $457 million and making it the fifth highest-grossing horror franchise in North America. Just in time for Halloween, here are ten facts you might not know about the movie that showed us just how sadistic a tricycle-riding puppet can be.

1. The movie started as a short film. James Wan and Leigh Whannell wrote the story in 2001 and made a short film of just one scene to shop around Hollywood. The short eventually caught the eye of small studio Evolution Entertainment, who picked it up and later formed its Twisted Pictures horror division after the movie’s commercial success.

2. Pig guts make the perfect substitute for human insides. Sure, James Wan could have had a studio create some realistic innards, but the movie was already on a tight budget and stopping by the local butcher shop was much easier. Pig intestines were used for the scene when Amanda stabs her cell mate and has to dig through his guts to find the key to her reverse bear trap.

3. Limited time and money didn’t stop the movie from hitting a big payoff. The movie was originally intended to be a straight-to-video release, which is why it had a budget of barely one million dollars. James Wan shot the film in just 18 days, and after showing the film at a few screenings and getting a positive response from audiences, Lionsgate decided it would make for a good feature film to roll out at Halloween. The gamble paid off: Saw pulled in $18 million during its first weekend at the box office and had secured its sequel by the following Monday.

4. The movie was filmed inside a warehouse because it was cheap. James Wan had to make his budget stretch and couldn’t afford to shoot any exterior shots, and was forced to film the entire movie inside. Wan and co-writer Leigh Whannell were confident they could make a low-budget horror movie after watching The Blair Witch Project and Pi and explored different single room locations for shooting the movie. Before deciding to have Adam and Lawrence locked up in a bathroom, Wan and Whannell considered having two characters trapped in an elevator and shooting the movie through a security camera’s point of view.

5. The film first received an NC-17 rating because of its lighting and sound. There were a few gory scenes that rattled the MPAA’s nerves — Amanda’s intestine digging and the fat guy struggling through the barbed wire had to be shortened — but the main issue was the movie’s tone. The original version that was shown at the Sundance Film Festival had creepier fluorescent lighting and an uneven sound that didn’t sit right with the MPAA film board.

6. No time for rehearsals. Because Wan had a limited budget and little time, there was basically zero room for the actors to rehearse their scenes on set or with each other, which lent itself well to the film’s gritty and ragged feel. Wan told the A.V. Club that he wanted to do an Alfred Hitchcock style of filming, but that was nearly impossible because of the time constraints:

“It was a really tough struggle for me. Every day, it was me fighting to get the shots I did not get. I had high aspirations, but there’s only so much you can do.

Danny Glover and Shawnee Smith each completed their scenes in a single day of filming.