During the first scene in Myrna Warren's apartment, there is an extended shot with a hair caught in the lens at the bottom of the frame.
When Peter Warren enters his wife's bedroom the second time, he fails to notice a dead body lying on the floor until he is well inside. The location of the body is such that he would have seen it as soon as he opened the door.
When Peter Warren goes to Myrna Warren's front door for the first time, his right foot slips to the right as he steps onto the front porch area.