In an interview, Alex Wolff explains that he wanted to actually break his own nose for the scene where his character slams his head into a desk. Director Ari Aster respectfully declined that offer and told Wolff they'd give him a soft, cushioned desk for the scene. When it was time for the scene to be shot, Wolff slams his head into the desk only to discover that the top was foam and the bottom was hard. He dislocated his jaw (which is a previous injury the actor has had) for the scene.

Throughout the film, several words can be seen scrawled on walls. At one point, there are two words, LIFTOACH PANDEMONIUM. Liftoach is an English transliteration of the Hebrew word 'To open'.

According to Alex Wolf, the original cut of the film could have easily pushed over 3 hours. Mostly consisting of more family dialog.

Director Cameo (Ari Aster): the voice on the phone calling Annie about her exhibit date at the Archer Gallery.

Allegedly a trailer for the film was accidentally shown at a screening of Peter Rabbit (2018) in Australia. However, a very similar event supposedly happened in 2007, where a trailer for The Hills Have Eyes Part 2 was allegedly shown to a theatre full of small children ( source: moviefone.com/2007/04/06/theater-accidentally-shows-hills-have-eyes-2-to-little-kids/amp/ ) Similar stories have been reported several times since then, even reported by reputable news sources, with a graphic horror film allegedly being shown to a group of small children, who were at the theater to see a kids' movie. In all alleged instances, the theatre is said to give free movie vouchers for all present. The similarities of these stories have made some speculate that it is nothing more than an urban legend.

Ari Aster was heavily influenced by the film The Cook, the Thief, His Wife, and Her Lover (1989).

In Peter's first scene at school, the words "Escaping Fate" is on the chalkboard with the teacher discussing it. This is a reference to Halloween (1978), where the main character discusses the same thing in class. Appropriately, this movie was released the same day as the trailer for Halloween (2018).

The entire interior of the Graham house was built on a sound stage.

This film is director Ari Aster's feature debut.

Toni Collete (Annie) is 22 years younger than her on-screen husband, Gabriel Byrne.

This was the fourth A24 movie to get a wide release after The Witch (2015), Free Fire (2016) and It Comes at Night (2017).

The film premiered on January 21, 2018 at the 2018 Sundance Film Festival in the Midnight section.

Filmed in Utah Film Studios in Park City Utah

Gabriel Byrne worked with Alex Wolff in the HBO tv series "In treatment" (2008-2010), where they also played father and son.

Pain on, the demon the film is revealed to be about, is a demon who was cast into hell along with Lucifer and other heretical angels. Paimon is considered one of Lucifer's most devote warriors. Paimon is often depicted as having a female appearance but is actual male, which is why, in the film, the demon is first inside the daughter Charlie, and then later inside the son. It also states in ancient texts that when Paimon approaches, you can here a strange sound similar to the clicking noise that Charlie makes.

The language spoken during the "invocation" that is given to Toni Collette is a combination of Hebrew and Enochian.

Charlie is eating a Dove candy bar when she cuts off the bird's head.

During the party scene, just as Peter enters the bedroom to smoke pot, some kids are watching a black and white video on a laptop of someone being beheaded on a guillotine - foreshadowing the film's multiple beheadings.

During the therapy session Annie tells of a troubled family history that she had largely kept to herself, because she did not want to "put more stress on the family". It is suggested that the family had been under the influence of the cult for a long time and hence that Annie was the one suffering for the longest time. During the films finale, Peter gets to see with his own eyes what had been manipulating his mother all those years. The song playing over the end credits, "Both sides now", thematically relates to this series of events. The song contains the line "I've looked at life from both sides now" which could suggest, that Peter was now able to see things from his mother's point of view. The song also contains the line "Tears and fears and feeling proud, to say I love you right out loud" which could suggest, that Peter finally understood that his mother actually did care for him and now was able to return those feelings, in spite of all he had been put through.

Early in the film, Charlie cuts off a pigeon's head outside her school. This foreshadows Charlie's accidental decapitation later in the film.

At the end when the life-sized figurine of the demon Paimon is shown, the fingers of its right hand are positioned in a way that Jesus is often portrayed as doing in medieval paintings (pointer finger and middle finger out and together, other to fingers curled in a fist, and thumb parallel but slightly curved), but on Paimon, he's holding it upside down. The medieval and ancient hand gesture is used as a representation of Jesus, so like crosses being inverted, Paimon is using this to disrespect Jesus. Also, Paimon is wearing a halo with rays coming out of it like a sun. This halo is also seen in depictions of Jesus, thus meaning those worshiping Paimon believe he is the true savior.

Toni Collette's character Annie says in group therapy that her mother had DID. This is the same disorder that Collette's character had in the series "United States of Tara."

The smiling man from the grandmother's funeral can be seen in a dark doorway towards the end of the movie.

Toni Collete starred in a Showtime show by Diablo Cody called United States of Tara in which she played a character who suffered from DID (dissociative identity disorder). In the movie, Annie Graham (Toni Collette) says her mom had DID.

When trying to run a seance to contact Charlie. Annie says, "Charlie? Charlie are you there?" These words are also spoken during a popular game from YouTube where people attempt to summon a demon or ghost named Charlie.