How / why did Steve catch on fire when Ann threw the sketchbook in the fireplace?
Earlier in the movie, when she tried to burn the book (as instructed from reading the Spiritualism book), her arm caught fire (implying that she was indeed possessed after the seance scene which had implied it then as well), but later when she puts the book in the fire it is Steve who catches fire and dies (seemingly ignoring the rules that the movie had set up earlier (if the spirit could have set anyone on fire at any time, why not set the whole family on fire from the start, use the cultists to freak Peter out enough for the spirit to possess, and be done with it?)). I may not have been paying enough attention, but it did not seem like an explanation was ever given or implied for this (seemed like pure plot convenience).
Some arguments and counter-arguments
As a sort of supernaturally-influenced-coincidence explanation: I know she throws some kerosene on the book while he's holding it, however it never really gets on his person that much and he is never near the fireplace in this scene.
My best explanation for why it happened (will follow with reasons why this seems incorrect):
- After the seance ceremony, Ann is possessed (or at least inhabited) by the spirit Paimon. She remains so until
- she later finds her mother's body in the attic. Steve comes home and Ann asks him to see if there is really a body in the attic, he goes up and we hear him freak out.
- At this point, the spirit (which the movies tells us wants a male body) moves from Ann into Steve in this moment of weakness (since (I think) the movie says something about 'needing a vulnerable host'). This would also explain a bit more why he was more blameful of Ann when he comes down from the attic and reluctant to burn the book himself (even though he was witness to the supernatural happenings during the seance).
- So when Ann later burns the book, it does obey the rules the movie set up earlier by burning Steve, but then
- (in Ann's state of shock and weakness right after) the spirit is able to move right back into Ann (and take full control).
Two reasons why this is probably not the case
- Why not Peter at this point? At the point in the movie before Steve goes into the attic, Peter is already more (visibly (to avoid falling into pure speculation)) freaked out than the dad is. If the explanation above is correct, then why not move into Peter right then? It is even implied that the spirit wanted Peter and not the dad by Joan at the end in the tree house where she says something to the effect of 'we got you this young, healthy male body'. Plus the fact that the spirit shows little interest in Steve throughout the whole movie (unlike with Peter).
- Seems inconsistent with the rest of the movie's level of immediate (or at least explicit) foreshadowing of supernatural stuff. What I mean by this is that throughout the whole movie every supernatural thing is 'accounted for' near to before it happens (eg. the symbol on the pole as they drive to the party that Charlie is later decapitated by, Peter daydreaming and seeing the "spirit light" in the hall before slamming his head on the desk, and all the weird things in the house environment (like the nightmares and general animosity between the family members) all tied up by the mother's body and the symbol in the attic) for things that might otherwise look like the-spirit-did-it-somehow plot conveniences.
Is there ever a solid explanation (or Paimon-symbol-on-the-telephone-pole level hint) in the movie for why Steve ends up catching on fire in the end? Any in-universe reason given by the writers in an interview or something for why this happens?