At around the 1:20 mark when Maya is driving the ambulance, her obviously golden nail varnish changes to black nail varnish.
During the ambulance scene, the frequency and intensity of the ambulance lights changes. This is because parts of the ambulance scene were re-shot.
As Maya is approaching the dead body of Pin-Up (after the ambulance scene), blood is pouring out from under her head. This blood isn't as obvious in later shots.
Throughout the film, Maya's scars change between two variations. This is because large parts of the film were re-shot (including the morgue scene, the farm sequence, and parts of the ambulance scene).
When Maya is in the bathroom of the barn, you can briefly see that the door has a hole in it before Scarecrow breaks in.