Continuity mistake: When "B" accidentally pulls the leg off of the dead dog, the position of it in her hands changes between cuts.
Continuity mistake: Towards the end of the film the amount of monkshood inside Brigette's needle changes several times.
Plot hole: The scene where the sisters are talking about killing the popular girl in class during P.E. during a game of Lacrosse, Bridgette is pushed into the body of a disemboweled dog. Everyone then starts to freak out seeing the dead animal. How could anyone, the students, teachers, grounds-keeper, not see that corpse until Bridgette was knocked into it?
Continuity mistake: When Brigitte pries the photo of the werewolf out of her Polaroid camera, in the first shot, her hands are extremely pink/red. (I'm not sure if it's the lighting, or if it's meant to be blood from cleaning off her sister.) Regardless, the color is very obvious. When it cuts to a closeup of her hands holding the photo, suddenly, he skin is perfectly white and not pink. It cuts back to the first angle, and they are very pink/red again. Clearly the closeup shot was filmed at a different time.
Continuity mistake: When Ginger and Brigitte are buying tampons, when Brigitte says "This one comes with a free calendar" she turns around to look at Ginger. The way she is holding the box of tampons and her laptop (I think that's a laptop?) changes instantly between cuts. Ginger also moves about a foot or two back between the same cut.
Continuity mistake: When Jason is trying to get Ginger to smoke with him at the store, he leans in and says " nothing quite takes the edge off like a good toke!" His face is only about 4-5" from her face to her left. It then cuts to another angle, and we see he's longer that close to her in fact he's not even onscreen, meaning he moved back instantly at least a foot between cuts.
Visible crew/equipment: When Ginger and Brigitte find the dead dog in the park while they're going to prank the mean-girl, there's a dramatic shot where the camera moves between them and tilts down to reveal the dog. When this happens, you can blatantly see the shadow of the camera move over Ginger's back/arm.
Continuity mistake: In the beginning when the mom discovers the dead body of her dog, she walks in front of an outdoor playhouse in a wideshot. It then cuts to a medium shot of her screaming. Between shots, she is suddenly standing in a different spot entirely... she goes from standing in front of the corner of the playhouse, to being dead center in front of it. She also seems to be several feet closer to it.
Visible crew/equipment: When Jason approaches Ginger and Brigitte and suggests they should "get together," you can subtly and briefly see the shadow of the camera on the back of his head. When it cuts to the opposite angle, there's nothing else behind him that could be casting the shadow. (It happens very quick and can be hard to catch).
Continuity mistake: When Ginger and Brigitte are smoking in the school field in the beginning and notice Jason checking Ginger out, they turn around. Ginger hand (holding the cigarette) goes from up near her chest to down by her waist instantly between cuts as they turn around. Between the same cut, Brigitte's hand also goes from exposed to covered by her sleeve.
Continuity mistake: In the classroom at the beginning, when Jason asks "Can we see the ones with Ginger again?", watch closely. His hand instantly raises between cuts. Additionally, the girl behind him goes from having her arms down, to having one up under her chin, to back down again between cuts.
Continuity mistake: When Ginger and Brigitte are taking a photo of Ginger "impaled" on the fence right before the opening credits, the amount of blood on the fence instantly changes between cuts after Brigitte says "Too much blood and I can see your gonch!" (Suddenly, much more blood appears on the fence posts on the right side of screen).