When it was released theatrically in the fall of 2009, Paranormal Activity surprised everybody with its primitive thrills and huge box office take. Made on a micro-budget of $15,000 by first-time director Oren Peli, the film grossed $193 million worldwide and spawned five sequels, including October’s upcoming 3-D installment, Paranormal Activity: The Ghost Dimension. Here are some spooky facts about the spine-chilling first film.

1. PARANORMAL ACTIVITY IS THE MOST PROFITABLE FILM OF ALL TIME, BASED ON RETURN ON INVESTMENT.

Often compared to The Blair Witch Project because of its low-budget nature and huge grosses, 10 years after The Blair Witch Project’s release, the original Paranormal Activity ousted the earlier horror film as the most profitable movie, based on return on investment (ROI). The Blair Witch Project cost about $60,000 to make whereas Paranormal Activity’s initial budget was just $15,000. Blair Witch grossed $248.6 million worldwide, which comes out to a 414,233 percent return on investment. After grossing $65 million, it was calculated that Paranormal Activity made a 433,900 percent ROI. Of course that doesn’t factor in its final worldwide gross of $193 million (which, if you do the math on that total, works out to a 1,286,566 percent ROI).

2. OREN PELI HAD NEVER WORKED ON A MOVIE BEFORE PARANORMAL ACTIVITY—LET ALONE DIRECTED ONE.

His background was as a software developer, a skill that provided him with the technical know-how to shoot a low-tech movie. “I’ve always been very comfortable with computers and software, so one thing that’s made my life easier is the fact that I was very quickly able to figure out how to edit the movie, how to do the audio mixing, and the CGI that’s in the movie,” Peli told Moviefone in 2009. He used a home movie camera, filmed in his own house, hired unknown actors who helped with the production, and edited down 70 hours of footage.

3. THE MOVIE KICKED AROUND THE FILM FESTIVAL CIRCUIT FOR A COUPLE OF YEARS.

The movie premiered at Los Angeles’s Screamfest in 2007, where Katie Featherston won an award for Best Actress. Producer Jason Blum helped Peli get an agent, and they started submitting the film all over town looking for a distributor. Though they failed to get the movie into Sundance, it did screen at another Park City festival, Slamdance, in January 2008. DreamWorks wanted to remake the film, but eventually decided it was scarier as is.

4. PRODUCER JASON BLUM WAS NOMINATED FOR A NON-PARANORMAL OSCAR.

Around the time of Paranormal Activity’s film festival circuit success, Jason Blum was working for Miramax and hooked up with Peli to help him edit the film. Blum earned a co-producing credit on the first film (and its subsequent sequels). Besides producing other horror franchises like Insidious and The Purge, Blum co-produced Best Picture Oscar nominee Whiplash, and he also won an Emmy Award for executive producing Ryan Murphy’s The Normal Heart for HBO.

5. OREN PELI’S FOLLOW-UP FILM BOMBED AT THE BOX OFFICE.

A few weeks after Paranormal Activity became a smash hit worldwide in the fall of 2009, Paramount secured the rights to Peli’s next found footage film, Area 51. Budgeted at $5 million, the film got held up for six years until it was released on May 15, 2015, with a week-long limited theatrical run at Alamo Drafthouse theaters and on VOD. The film, which was released in just 16 theaters, only managed to gross $7,556—a far cry from Paranormal Activity’s phenomenal ticket sales.

6. KATIE FEATHERSTON IS THE ONLY ACTOR TO APPEAR IN EVERY INSTALLMENT.

A rather inexperienced actress before auditioning for Paranormal Activity, Featherston reappears in the sequel and has cameos in all of the films that have been released so far, and possibly the upcoming sixth (and purportedly final) movie. She also appeared in three episodes of Peli’s short-lived 2012 series The River. “No more day jobs, lots of scripts, it’s just overwhelming,” Featherston told Dread Central of her newfound fame in 2009. “Walking into an audition room now is so different than it was six months ago.” Despite getting a lot of attention after the success of the first film, according to her IMDb page she hasn’t acted in much apart from the Paranormal sequels.

7. STEVEN SPIELBERG THOUGHT HIS DVD OF THE FILM WAS HAUNTED.

As the urban legend goes, Spielberg, whose DreamWorks Studios was considering distributing Paranormal Activity, took a DVD of the movie home to watch, but then got freaked out when the door to his bedroom locked by itself. “So the whole story about how the doors to his bedroom got locked from the inside ... personally I believe it,” Peli told Moviefone. “It’s not something the marketing department just came up with before releasing the movie.” Spielberg famously carried the DVD to work in a trash bag because he thought it was haunted. Despite the shock, Spielberg loved the movie and suggested a new ending that was used in the theatrical release.

8. PELI FILMED THREE ENDINGS TO THE MOVIE.

This YouTube video simultaneously shows all three endings, with the original being twice as long as the others. The original entails cops coming into the house the next day and shooting and killing Katie. The alternate ending features Katie gruesomely slitting her throat, and the theatrical ending is what most people saw in the theaters: Katie supposedly killing Micah and becoming possessed by the demon. According to Entertainment Weekly, there was also an ending they never filmed: “A possessed Katie corners Micah and bludgeons him with his precious camera, while viewers watch from the camera’s POV.”

9. THE MOVIE KICK-STARTED THE FOUND FOOTAGE GENRE.

Though 1999’s The Blair Witch Project was hardly the first found footage film (many say that distinction belongs to 1980’s Cannibal Holocaust), it generated new interest in the format. Still, audiences would have to wait until 2008’s Cloverfield, which was a modest hit, and another year for Paranormal Activity (which was filmed in 2006) to start seeing found footage films emerge as their own subgenre. To this day The Blair Witch Project remains the highest-grossing found footage film of all time, though.

10. ALEC BALDWIN AND STEVE MARTIN PARODIED PARANORMAL ACTIVITY AT THE 2010 OSCARS.

You know something has invaded the pop culture mainstream when it starts being parodied, which is exactly what Oscar co-hosts Baldwin and Martin did during their opening segment at the 2010 Academy Awards. The premise was that they just happened to be sharing the same hotel bed, and Martin set up a camera to record their sleeping habits. Martin thrashes around all night and at one point gets up and slaps Baldwin. No ghosts here; just terrible sleeping companions.

11. THE EXORCIST DISTURBED PELI SO MUCH THAT HE COULDN’T WATCH GHOSTBUSTERS.

“I saw it [The Exorcist] when I was 11,” Peli told The Guardian in 2009. “It totally freaked me out. After that I couldn’t watch any movie that had anything to do with a haunting or a ghost. I was in my mid-teens when Ghostbusters came out and although I knew it was a comedy, I couldn't handle the idea of it. I didn’t see another horror film until I was well into my twenties.” Peli’s fear of the unknown, especially the strange sounds he heard in his own house, partially inspired him to make Paranormal Activity.

12. PARANORMAL ENTITY TRIED TO CAPITALIZE ON PARANORMAL ACTIVITY’S SUCCESS.

Two months after Paranormal Activity was released, a film called Paranormal Entity used a similar surveillance format to create a story that may or may not be real. Three more movies were made to coincide with the Paranormal sequels: 8213: Gacy House (Paranormal Entity 2), Anneliese: The Exorcist Tapes (Paranormal Entity 3), and 100 Ghost Street: The Return of Richard Speck (Paranormal Entity 4). None of them managed to match the success of the series they were trying to emulate.