Revealing: In the scene where Hallie trashes Annie's cabin and the huge water balloon is about to fall on Annie's head, the camera is at a downward view and Annie clearly steps into the trail of the balloon instead of jumping away.

Continuity: When Sammy runs to Hallie in the Stafford Hotel elevator, he jumps over (or, more accurately, through) a baggage cart that was not in the previous wide shot.

Revealing: In the scene where Hallie is about to pierce Annie's ear, Annie puts the apple underneath her earlobe and Hallie puts the needle in - you can clearly see that Annie's ear already has a hole in it.

Revealing: After the two girls are finished playing poker in the cabin and Annie lost and had to jump in the lake naked, you can see the outline of the bathing suit she is wearing.

Continuity: In the scene where Hallie and Annie are in the isolation cabin, you see the bucket that the water is dripping into from the leak in the roof, on a stack of books. After the wind blows all of Hallie's pictures off the wall they are sitting on the ground picking them up, Annie is seen picking up Hallie's little animal (Cuppie) right next to the bucket of water, which is now on the ground with no stack of books to be seen.

Continuity: In the scene where Dennis Quaid sees Elizabeth and falls in the pool, its broad daylight, but when she helps him and they're sitting down, its twilight and there are a lot of lights on, but when they see his fiancée they stand up and it's broad daylight again.

Revealing: In the scene where Annie has to jump in the lake "butt naked," she's standing on the dock, and at one point she has noticeably pierced ears. But Annie (the Londoner) is the one who didn't have pierced ears until after the girls discovered their twinness.

Continuity: In the scene where Hallie wants to get a popsickle/lemonade, her hair bobble is green, but in the next shot it is white and then changes back to green again.

Continuity: In the scene where Hallie arrives in San Francisco she is shown getting out of the car and the door is closed, then in the close-up shot the car door is open in the background.

Revealing: When Meredith meets Nick and Elizabeth at the pool, Hallie comes up on her left and says, 'Hi, Mer.' Then Annie comes up on her right and says, 'How's it going?' Meredith shrieks as she looks from one girl to the other and you can tell that Annie is not really there, because Meredith is looking over her head rather than directly at her face, which she does with Hallie.

Continuity: In the car, before entering her mother's house, Annie is wearing a plastic watch, but when she hugs her mother she is wearing a metal watch.

Continuity: When everyone is saying their good-byes at camp, Hallie (as Annie) takes the passport and the small carry-on and turns to get in the limo. The shot switches so you can see the limo, and Hallie (as Annie) is holding the carry-on in the other hand.

Continuity: In the scene where Annie playing Hallie is being introduced to Meredith by the pool, it shows Nick wearing sunglasses, but in the next shot of him he is not.

Continuity: In the scene where Annie is entering her home in London, she puts her hand on the doorknob and pushes the door open. In the next shot when it shows the entryway with the door opening, there is no doorknob.

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.

Factual error: If you have ever actually seen London then you can see that the route Hallie takes to get to the house would take you all around London.

Continuity: The scene is by the pool at the hotel in San Francisco.  He has just emerged from the water and is sitting on a lounger.  Bits of the scene were clearly shot at markedly different times of day, as the light changes noticeably in colour and direction of shadows.

Other: When Hallie is trying to stop Marva from entering the Navajo bunk, there is one shot where Annie glances up at the bucket of chocolate hanging over the door. Since the prank was set up while Annie was asleep, she'd have no way of knowing it was there.

Continuity: When you see the limo driver taking out Annie's luggage, the limo is right next to the luggage, but when Martin is about to leave you see the limo much further away from the luggage.

Continuity: When the twins are standing on the steps of the isolation cabin, talking about their familes, Hallie, one time is not looking at Annie - her eye-line for the special effect is off.