(at around 14 mins) When Will leans the ladder against the house the rungs are facing backward, the rope pulley on the right hand side. In the following shot, from his POV looking at the footprints, the ladder has been flipped to the proper position.
When Will is following the footprints outside the house, the string on the left hand side of his hoodie pops in and out between shots.
When Will goes to room 308 in the halfway house there is no crucifix on wall, in the next shot when Martin enters the room a large one appears to the left of the window.
Will is walking in town and looks into the café as a man and a woman - the woman is wearing red boots - walk towards him. He goes in, talks to the police officers and leaves a few moments later. When he does, the same couple are walking towards him again in the same direction.
Chapter 8 time 0:32:43. When Will comes up the stairs his wife is Spackling the hallway wall that is reverse to the master bathroom wall. Wills Point of View does not match the floor plan in the previous chapter. As Will comes up the stairs the reflection in the mirror reveals a door that is not in the floor plan in Chapter 7.
In the diner where Will is asking the police officers about the murders, the front shot of the officers is flipped as indicated by the text on the menu in the background as well as the seating of the officers switching between shots. That's because it's being seen through the mirror behind the counter at the diner.
When one of the girls is playing the piano, the song heard is Beethoven's "Für Elise" (For Elise). Her arm movements clearly reveal she is not playing the song.