Revealing mistake: The oil lamp carried by Mary when she first finds Colin has a flame that never flickers, and is likely an electric lamp.
Revealing mistake: When the boys' rival team challenges them, all the boys throw their gloves down, except Yeah-Yeah. When they all go to pick them back up, Yeah-Yeah has to pretend to pick it up.
Revealing mistake: At the end of the decisive game, the bad guy hits a deep foul ball. During that hit, they show the ball against a black background. If you look very closely at the bottom of the screen, you can see a hand throwing the ball.
Revealing mistake: When Wyatt Earp and the actress, whom he marries later in the movie, meet on horseback, they go on a fast paced ride that concludes after going down a steep hill. If you look at the actress' feet, you will see she is riding side-saddle - a very difficult feat considering the riding they do. If you look closely you can see her real leg, safely on the other side of the horse. The side-saddle leg must be fake.
Revealing mistake: During the "grand finale" fight scene, which takes place on the underside of an overturned helicopter hanging from a cliff, a few frames show the rigging that is holding the helicopter in place.
Revealing mistake: When Jason (in Robert's body) is shot in the head at the end of the hall, a close up reveals the bullet hole to be obviously just makeup. (01:05:35)
Revealing mistake: When Henry throws the dummy off the bridge, watch the rear window of the gray car; it explodes before being hit.
Revealing mistake: In the final scene when Annie and Sam are exiting the observation deck coming towards the elevators, the New York skyline backdrop which should be visible behind them is missing, and the entire sound stage wall can be seen beyond the observation deck safety railings instead. 'Although the exterior and lobby of the Empire State Building, 350 Fifth Avenue at 34th Street, are the real thing, a slightly larger replica of the Observation Deck was built in a hangar at Sand Point Naval Base on Puget Sound just northeast of - where else? - Seattle.' https://www.movie-locations.com/movies/s/Sleepless-In-Seattle.php. (01:39:35)
Revealing mistake: When Robo gets his arm chopped off by Otomo, he stands up and in Robovision, you see that he needs power, but you cannot see Otomo who is supposedly right in front of him.
Revealing mistake: Doesn't it seem odd to anyone that the crops hadn't been reaped by Thanksgiving in South Dakota?
Revealing mistake: Near the beginning of the film, an axe is thrown at a priest. The axe should rotate as it travels, because the head is heavier than the handle. But it hangs upright as if drawn by a wire.