When Bonnie goes back to gene therapy she has bandages on, that weren't shown in any other part of the movie. They also extend up her neck, but scars are never seen on that part of her body, even when her hair is up.
In the French lesson, the teacher wrote on the board "Si vous aviez faites vos devoirs, vous comprendriez" (which means "If you would have done your homework, you'd understand"). Actually, it is supposed to be "Si vous aviez FAIT vos devoirs, vous comprendriez".
When Bonnie first goes to gene therapy, the scars are all over her back and down her left arm. However, when the four of them are strutting down the school hallway, her short sleeved shirt reveals no scars on her arm. The scars are back down her arm when she goes the second time to the doctor.
When Sara walks in to the room at the party where Nancy and Chris are on the bed, as soon as Nancy appears to be in her own form again, you can see that her lipstick is smeared almost to the point of being completely gone. However, when she gets off of the bed and begins yelling at Chris, her lipstick is perfect.
When Sarah & Chris are sitting in his convertible on the night they're supposed to go out to dinner, it is obviously dark out & night time. However, when Sarah runs through the woods to get away from him, it is daytime with a blue sky seen through the trees.
In the "green traffic lights" scene, scenes shot from the passenger side of the car show Nancy (who is driving) holding her arm up and leaning out the window with a cigarette in her hand, but the scenes shot from the driver side show her left arm resting at her side.