Hereditary is connected to The VVitch
Both share many similar story elements already and were both produced by A24. What if The Witch was setting the stage for Hereditary? The Devil seen in The Witch could be the demon king Paimon in the 17th century, only without a host and forced to take on different forms to interact with the world. The witches serving him at the end are a past incarnation of the cult that now serves him, who also seem to wield supernatural power. The story has vague undertones of trans identities and transitioning.
Even if this was not the intention of the director or the actors, Peter's role in the story shares striking similarities to a trans man coming out to his family. If this is taken into consideration, Charlie's accidental death by his hands symbolizes "killing" his past self, which he sees as terrifying. Leaving her body to be discovered by his mother out of shock can also be seen as being outed, as he makes no moves to remove Charlie's corpse out of pure terror. His mother blaming him for the death of her daughter is a phrase that many unaccepting parents have used against their transitioning children.- On top of that, Charlie having an androgynous name and her grandmother flat-out telling her that she should've been born a boy plays heavily into this. Of course, it's because Paimon needs a male host, and Charlie was the only relative that could fill that role due to Annie keeping Peter away from his grandmother, but the implication of not being the way everyone wanted you to be is deeply reminiscent of a trans person's struggle with their identity.
Everything after Charlie Dies is Annie's psychosis.
The demons aren't real, it's all Annie's mental illness manifesting and breaking from her grief. Her mother was mentally ill. After all, mental illness tends to be...Hereditary.Peter was an unwanted child to Annie from the start. Admittedly, so was Charlie—at least at one point—and it's hard to gauge if Peter was moreso, when these sentiments boil to the surface only after Charlie's death. Unlike Charlie, however, Peter looks rather noticeably not blood-related to Steve.- In turn, the camera's notable focus on Bridget, as she visibly condoles for Peter, might suggest that Paimon is going to extort her sympathies; and get Peter close enough to her, to use her to continue the bloodline. However consensual this could possibly be on her part, it's unlikely that she'd leap to spawn and possibly die for another human host.
- One must also wonder what kind of "hard life" Ellen had lived, that as Annie mentions could be connected with her abusive ways.
- Annie's final complaint in her tantrum against Peter is that nobody who hurts her ever admits what they've done. She's clearly talking about her own past, not the current issue, but she's the only one who can know that in that scene. Combined with her rant in Ellen's eulogy about how she'd never admit to being wrong or at fault and Ellen's ruthless pursuit of wealth through demon worship, it paints a picture of Annie as being victimized by a narcissistic parent. Combine that with how Ellen was likely too old to bear children by the time Peter was conceived, and the dots start lining up (Full disclosure, this troper thought that this trope was the intended interpretation). If Annie 'never wanted to be Peter's mother' because she didn't consent to the conception in the first place, that explains her resentment of Ellen and their "talking, then not talking, then talking again" relationship: if Annie's rapist was never punished (or worse, if she suspects that Ellen actually had a hand in her rape, she could never prove it and Ellen would never admit it), naturally she'd have no closure about the event itself, and not hearing Peter, son of that rape, just apologize verbally and acknowledge his role in Charlie's death, is re-traumatizing her, and she has no way to communicate it without also admitting her real feelings about her son's birth.
Charlie ate the nuts on purpose
A deleted scene shows Charlie and Peter before entering the party, highlighting how uncomfortable she is with this situation and how even if she waited outside, she'd be stuck there since Peter is her ride home. Additionally, the screenplay mentions explicitly how nuts were visibly an ingredient and how Charlie hesitated for a moment before swallowing. So it's not impossible that she was staging a Wounded Gazelle Gambit to force Peter to take her home. Of course, this backfired because she underestimated the severity of her nut allergy. Why? Some mental condition combined with the total nonchalance Annie and Steve were shown to regard her allergy with.