- The first trailer features two notable shots of decapitation, so it's no surprise that two characters of the film, Charlie and Annie, die this way.
- At the funeral, Annie delivers a eulogy saying that Ellen had "interests" that even Annie didn't know about.
- Charlie tells Annie that Ellen said she always wished Charlie had been born a boy.
- This exchange between Annie and Charlie:You don't think I'm gonna take care of you?But when you die.
- Her grandmother had been prepping her for Annie's death and her subsequent resurrection, possibly after Ellen's own death. Charlie knew, at some point, that she would be alone in the world.
- Annie mentioning in the support group that her "schizophrenic" brother claimed that their mother was attempting to put people inside of him. This foreshadows that the cult is attempting to summon Paimon inside of Peter.
- After Ellen's funeral, Annie goes through a box of her possessions. In one of the boxes, she finds a book about spiritualism and the occult. It isn't until much later in the movie that this is revisited and revealed to be relevant to Ellen's sinister plans and her involvement in a demon worshiping cult.
- The necklace that both Annie and Ellen are seen wearing is the symbol of Paimon. The symbol is also found carved into the same telephone pole that decapitates Charlie as well as painted in blood in the attic.
- One of the horrifying little sculptures Charlie makes is headless figurines bowing to a pigeon-headed figure with a crown, which mirrors the horrific tableau she herself becomes a part of at the climax.
- We learn that Annie kept her mother away when she was pregnant with her first child Peter but she let her come back when she was pregnant with Charlie. Free of her mother's presence, Peter is born normally but Charlie gets possessed by Paimon when she is exposed to her grandmom.
- The hand gesture Peter makes while he's possessed in class is later seen in the form of a staff held by the statue of Paimon.
- During Peter's literature class early in the film, the teacher asks whether a story is more tragic if the characters have a way to escape or if it's more tragic if they never had a chance to change their fate. Annie thinks by destroying Charlie's sketchpad, she can free the family from the curse. It doesn't, Steve dies, she gets possessed by a demon and decapitates herself, and Peter gets possessed by Paimon.
- Peter's literature teacher mentions two pieces of Greek mythology, Euripides's Heracles and the death of Iphigenia. In both of these stories, parents kill their children.
- Furthermore, it's mentioned that Heracles's flaw is that he was too prideful to admit his failings, and thus ignores all the signs of those failings being "literally handed to him". Annie ignores a lot of the signs that something is deeply wrong about her situation out of desperation to escape her pain, including a welcome mat that Joan owns that demonstrates she knew Annie's mother, her being handed an incantation that she doesn't understand to hold a séance, her family's growing dysfunction and discomfort as a result of her lashing out, and her own family history slowly beginning to mirror her current situation.
- Early on in the film when Peter is smoking in his room, you can see someone else breathing outside. Likely a cultist observing the family.
- Even the posters have gotten in on this. The poster above is very heavily shadowed so only Charlie and Annie's faces are visible, almost like their heads are floating in space, detached from their bodies...
- The tiny model in the same poster looks like a headless figure worshipping the pigeon's head, foreshadowing the presence of headless worshippers in the treehouse at the end.
- Charlie's picture of the crown-wearing pigeon mirrors the final scene of the film, where Peter is given a paper crown to wear after he becomes Paimon's new host. Even the cast on his nose looks somewhat like a bird beak.
- Charlie is wearing a fleece during the "who will take care of me?" scene, alluding to her role as the (first) Sacrificial Lamb of the film.
- In multiple scenes Steve is heard stating how cold it is, even if the other characters dont think so. Later on, hes lit on fire after the notebook is thrown in the fireplace.
Foreshadowing / Hereditary