Revealing mistake: When 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. (00:18:05)
Plot hole: The parents meet and get married on the QE II and then we jump to the girls getting to camp 11 years and nine months later. We learn their 12th birthdays are on October 11, so at the time of the camp (which must be around July/August) they are 11 years and around 9 months old. They should only be 11, given it takes 9 months to grow a baby, but instead they're nearly 12.
Suggested correction: Elizabeth James got pregnant sometime within the 11 years. Their parents sent them to camp in July because in October they both turn 12. So they are 11 years 9 months old.
The mistake is valid, but perhaps not specific enough about why. The opening scene takes place Jan 8, 1986 (as seen on the marriage licence). Then it says 11 years and 9 months later, which would mean in the next scene it's October 1997 (when it's July 1998). It's 11 years and 9 months after the twins' birth and/or the parents' divorce. But we're not actually shown that part.
Revealing mistake: When 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. (00:40:39)
Suggested correction: I've looked at it closely. I can't see a hole anywhere.
You can also see that Annie's ear is already pierced during the lake scene.
Continuity mistake: When 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. (01:29:40)
Suggested correction: Sorry. It looks bright to me the whole time.
When they're sitting, it looks darker than when he originally fell into the pool.
Continuity mistake: When 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. (00:18:20)
Revealing mistake: 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.
Suggested correction: Actually, Annie comes upon Mer first from Mer's RIGHT, not left. Hallie then comes up on Mer's left. Also, Meredith perhaps looks above Annie's head a little, but hardly noticeable.
Continuity mistake: When Annie and Hallie get out of the water bin after their fence match, the water stain on Hallie's vest changes patterns.
Continuity mistake: When 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.
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 mistake: 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 mistake: When 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. (00:29:07)
Suggested correction: The first shot of the bucket does not show the entire bucket so you can't see any books under it.
Continuity mistake: When Hallie wants to get a popsicle/lemonade, her hair bobble is green, but in the next shot it is white and then changes back to green again. (00:24:30)
Continuity mistake: 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 mistake: In the scene where Nicky and Annie are talking about him getting married, Annie's cowboy hat on the couch at her left changes position a few times. (01:05:00)
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: Placing Hallie and Annie alone in an isolation cabin without a counselor sleeping there to supervise is an enormous liability. No camp that cared about its reputation and about avoiding a lawsuit would ever put two girls in such a potentially unsafe situation.
Continuity mistake: 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.
Factual error: Copyright stamp at the end of credits reads MCMMXCVIII, that is the third M is superfluous.
Continuity mistake: When Annie got hit by the huge water balloon, she got herself drenched from head to toe. But in the next scene when both the camp leaders, as well as Hallie, were inside the bunk with her, Annie was completely dry.
Continuity mistake: When Annie and her friends are approaching the area where the fencing is taking place, all three girls are holding tennis rackets. The shot switches to the camp counselor and back to the girls. The African American girl is no longer holding a tennis racket. The shot goes back to the counselor and then to the girls again, where all three have a tennis racket again.
Suggested correction: The third shot of the girls does not show the black girl having the tennis racket again.
