Continuity mistake: When Hallie (posing as Annie) arrives in London, she is seen sitting on the left seat in the car when she's on her way home, passing by the various spots in London. However, when she reaches home, she is sitting on the right side of the car. Unless she was sitting alone, this is not logical as Martin was sitting together with her at the back of the car.
Continuity mistake: When Annie and Hallie are just about to play cards, Annie spreads all the cards out on the bed and turns them over and then back again. But in one of the shots you can see that it is Hallie who turned the cards over because her fingernails are painted and Annie's are not. (00:14:00)
Continuity mistake: In the opening scene, they show the lake and the little sign that says Camp Walden. There are boats under a roof top right in front of the pier. But in the scene where they show Annie jumping into the lake the boats are in a different location and the roof top is gone.
Continuity mistake: In the opening scenes where they show the camera girl about to take a picture of them, you can see that there are candles and a flower arrangement on the table. When they open the book to show us the picture of them the candles are gone and the flower arrangement is different. (00:03:25)
Continuity mistake: When Hallie is posing as Annie and is going to her mother's house for the first time, a piece of her hair is obviously sticking out on the side of her ear (It's very noticeable). When she gets to the front, and the camera angle changes, her hair is all perfect without any hair sticking out.
Continuity mistake: When Hallie arrives at the airport, Martin has a bouquet of flowers for her. He never hands them to her, but suddenly she has them and sets them down in order to do the handshake.
Continuity mistake: In the scene when Hallie meets Grandfather, there are two bottles on the desk. One is filled with alcohol and the other is not. During the next shot, both bottles are moved to the back table behind the desk and the bottle filled with alcohol is empty. (00:38:05)
Continuity mistake: When Hallie and Annie drag Meredith into the lake when she's asleep on the air mattress, the color of the air mattress is dark green. When Meredith wakes up with the bird on her chest, all of a sudden the air mattress is a two tone khaki color. When Meredith stands up on the air mattress in the next shot on the lake, the air mattress is now another shade of green.