When Steven and Curtis are strangling Timmy with the hose and Debbie watches; Debbie's hair goes from hanging in front of her shoulders, to then being behind her shoulders, then back in front again, between shots.
As Curtis is about to shoot at Joyce, Timmy tells her to duck to the floor - as she does, she puts her headphones down on the table. In the following shots, the position of them on the table keeps changing.
When Curtis kills Miss Davis by shooting her, she falls to the floor and leaves no bloodstains on the kitchen cupboards that she 'slid' down. In the next wide shot of her body on the floor, there is now a large bloody stain on the cupboards.