Revealing mistake: When in Boston, while walking through the park, Susan and her mother are obviously walking on a treadmill because the park background is moving way too fast for their walking speed.
Revealing mistake: When Mitch is driving "Susan" home from the airport, in one shot, the knob of the gear selector lever is visible above the dashboard, which means the transmission would be in Park.
Revealing mistake: When the "twins" are singing "Let's Get Together" they are standing side by side. Watch closely - because of the split screen, one twin's arm disappears for just a second when she swings it upwards. It actually happens twice - middle of song and end.
Revealing mistake: When Susan goes outside to sit on steps after the rain has stopped you can see her double siting on the bunk looking at her photo album.
Revealing mistake: When they are driving home from the airport, you can see the reflection of the green screen on the car hood.
Revealing mistake: Susan's camp friend with the light blond hair continually repeats the last word or line of the person before her, or mouths it to be ready for her own lines. In the dining room when the twins first see each other, Susan says something like "Whatever can I do about it?" and while she's saying that, the other girl is mouthing the words, then says her own line. She also does it in the shower scene, where they're talking about revenge, the other friend of Susan's says, "Give it to her good!" then this mimicker says, "Good. The old coventry treatment..."
Suggested correction: To start with the dining scene, she is not mouthing her lines, she only once moves her mouth a little but it wasn't to mouth the other girl's lines. And when she says "Good" she's not repeating the other girl's lines she confirming what the other girl said.
