Every parent's worst nightmare is just the beginning for Rachel's ordeal as in the aftermath of a tragic accident, she and her husband Anthony decide to move to the other side of the world to focus on their surviving twin son Elliot. What begins as a time of healing and isolation in the Scandinavian countryside turns into a desperate battle for the very soul of their son as an entity claiming to be his dead twin brother takes over Elliot — setting Rachel on a diabolical journey to unravel the horrible truth about her twin son.
This movie contains 30 potentially triggering events.
Goat heads are used in a "pagan" ritual.
A lot of this movie is ambiguous, right down to the end. So a lot of the "Yes" answers on this site refer to things that are implied or shown on screen but that may not actually have happened.
(Huge spoiler). The main character is mentally ill and suffers psychosis and in this state she beats her husband, almost kills him and then accidentally kills him.
There is, however, a scene where the camera moves at different angles as characters are standing on a swing. One of them appears to have motion sickness, and the scene might cause the same.