Mark gets the gun out of his holster twice within 2 minutes of the first scene.
When Lizzy is put out of her misery by Josh shooting her in the head, she is still moving in the wide shot revealing all the dead bodies.
The fake blood on the warehouse floor has clearly dried out during filming and has turned pink.
As Josh moves toward camera to say the line "are you afraid of the dark?" in the woodland scene, crew are clearly visible in the reflection of his sunglasses.