Corrected entry: In the swimming pool scene at the end of the movie, Jimmy forces Oskar to stay underwater by grabbing his hair and dunking him, and shortly afterward has his arm severed by Eli. One indicator that this is a fake arm is the fact that it is holding Oskar's hair backwards. Look closely and see how the fingers are pointing in Jimmy's direction, not towards the other side of the pool, which would be the natural position for them to be pointing towards.
Corrected entry: In the scene where Oskar first meets Eli at the building playground, Eli jumps down from the top of the jungle-gym and almost slips on the snow when she lands.
Correction: Naturally, the film was as close to character description as possible, given the fact that, in reality, people do occasionally slip in snow. Lina Leanderson, is no exception. Also, I'm sure they did many takes before using the one they used.
Correction: I am watching it now. He grabs his hair out of the water and his hand is facing the same way it is under water. This is not an error in the movie.