The concept is confusing till you get to the end and then it connects every piece that is shown till then. Looking back now no movie has given me the chills like this when I can't solve the mystery. I usually can identify the killer in many movies or the plot because I'm a little bit of a detective myself so it's simple if you think really and notice basic things. Leonardo and Mark Ruffalo were the perfect duo amazing casting overall. The deep emotions and the way Leo plays the character is way too intense it's like seeing something out of this world you don't think for a moment that he is acting but it's just real like watching a documentary or something the plot was played perfectly as you have no clue till it is revealed you cannot guess I don't think anyone could've guessed how it was gonna end.