The Exorcist is still terrifying audiences 45 years after it first hit cinemas.
The controversial 1973 movie told the story of the demonic possession of a 12 year old girl.
It was so scary that some cinemas provided vomit bags and the home video was banned in a number of countries.
However, it was a huge commercial success and the first horror film to be nominated for an Oscar for Best Picture.
The story off camera was just as eerie as the one presented to audiences.
Here's five fascinating facts about William Friedkin's groundbreaking movie:
1. Many of the cast and crew believed the set was cursed
A number of bizarre incidents attracted claims that the set was cursed, including a studio fire.
The fire burned all of the set apart from the bedroom of Regan, the possessed child.
Friedkin regularly brought in a priest to bless the cast and crew.
By the end of the film's production, nine people associated with its making had died.
2. The voice of the demon involved a radio actress and pigs
An actress named Mercedes McCambridge provided the voice of the demon.
There was nothing she wouldn't do to to achieve the gruesome gruffness, including adopting a diet of raw eggs, whiskey and chain smoking.
Unfortunately, McCambridge wasn't credited for her performance.
Recordings of pigs were also used to create a lot of Regan's moaning and grunting.
When the demon is finally exorcised from her body, the sound you hear is a group of pigs being led to slaughter.
3. Jason Miller's reaction to being vomited on is real
The projectile vomiting scene is one of the film's most famous and disgusting scenes.
Actor Jason Miller (Fr Damien Karras) was told the vomit would only hit him in the chest but the hidden tubing strapped to Linda Blair's chin misfired.
His reaction is authentic and was never edited. Unsurprisingly, the scene only required one take.
4. The vomit was pea soup
The green vomit was pea soup mixed with porridge, specifically Andersen's pea soup.
5. The head spinning scene was almost cut
Another famous scene is the one where Regan's head rotates 360 degrees, but writer and producer William Peter Blatty originally asked Friedkin to remove it.
The scene was filmed using a life-size rubber model of Linda Blair.
If you're obsessed (or possessed!) with horror films, you can watch The Exorcist at a drive-in cinema in Galway.
iRadio is delighted to announce that we're bringing back the drive-in cinema, in conjunction with Retro Drive-in Movies.
Catch The Exorcist on the biggest mobile LED screen in the world at Ballybrit Racecourse on Sunday, October 21st.
Here's the full schedule:
Friday, Ocotber 19th
Harry Potter and The Philosopher's Stone at 8pm
Saturday, October 20th
Harry Potter and The Chamber of Secrets at 2:45pm
Scream at 9:30pm
Sunday, October 21st
Harry Potter and The Prisoner of Azkaban at 3pm
Hocus Pocus at 6:45pm
The Exorcist at 9:15pm
Grab your tickets here.
