Revealing mistake: When Hallie and Annie are fencing with each other, Hallie forces Annie's sword into the air, and Annie runs towards the hay stack in the background to catch it. The sword lands on top of the stack of hay to the left of the screen and bounces out of sight; Annie then catches another sword that falls from above, that someone obviously dropped for her to catch.
Visible crew/equipment: When Dad shows Mum his wine collection and the wine from their wedding, you can see a microphone dangling right over Dad's head.
Character mistake: When Chessy confronts "Annie" when she's presenting her with the big breakfast, she's talking about when Annie was on the phone the night before. Then she says her father overslept, when she actually meant to say and "and you overslept," as the conversation doesn't make any sense saying that the father overslept. (00:58:00)
Factual error: At the hotel, Chessy's door to her room stays open after she goes into the other room to discuss the whole 'dad doesn't know' matter. In real hotels, the guest-room doors have auto-closing mechanisms for fire safety and security. The door would have swung closed and locked Chessy out, but even though this is a 4 or 5 star hotel which would be fully equipped as far as modernity's, it doesn't.
Continuity mistake: After Annie first meets Meredith (playing Hallie), when she's sitting in the red water floater, her necklace goes from tucked inside her bathing suit to out, then to in again.
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.
Revealing mistake: Annie and Hallie come downstairs at the hotel dressed in the same outfits, as their parents tell them to hurry before their mother misses her flight back to England. Nicholas Parker leans over and looks at one of the girls in the eyes and says "This one's Hallie" and she replies, looking straight ahead at him in the eyes. When the other twin speaks, she's looking straight ahead as well, which would technically mean she is looking at nothing.
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)Stephen Edmonds 1
Factual error: In the scene in which Annie and Hallie are fencing, it portrays it as though Annie does not win until she hits Hallie (effectively knocking her into the water). However, in a real fencing match, Annie would have won within a few seconds after they started. Once a person is backed off their end of the strip, their opponent automatically gets a point.