Continuity mistake: When Bill tells Selma he has no money, her hair changes from tied back, to down numerous times between cuts.
Continuity mistake: A drip of blood on Selma's cheek disappears and then reappears during the ride in Jeff's truck after she's killed Bill.
Continuity mistake: In the final scene where Bjork is singing the last song, as she starts strands of hair are in her mouth and over her right eye, but a bit later they are gone. Since her arms were strapped to her side she couldn't have brushed the hair out of the way herself.