Continuity mistake: During the wedding reception, George (Steve Martin) is called outside to meet with the police because there are too many cars parked in the street. Notice that the police car is curbside completely surrounded by cars. In fact, the whole street is packed with cars, making one wonder how the police car got up to the house.
Continuity mistake: When the car blows up at a rest stop, when the children run to Ice Cube, the boy is on his left. However, when they turn around and sit, the boy is on his right.
Continuity mistake: In one scene where the dad is leaving for work, he sees a dog and in that shot you see his mail truck and the door is open. Then you go to a close-up of the dog and when he runs to his mail truck the door is now shut.
Continuity mistake: When Harry puts Million Dollar Sticky on the TV, between shots Zinnia puts her sunglasses on twice. (00:18:45)
Continuity mistake: When Alan is trapped on the floor, and the game is placed over his head, Sarah rolls the dice which fall on the lower left corner. When the angle changes they've moved further to the right.
Continuity mistake: In the scene where Mindy is showing Spongebob and Patrick "Planktopolis," it shows a large fully-built statue of Plankton. A few seconds later the right side of the head is shown missing and still being worked on.
Continuity mistake: In the scene where Gabriel Byrne is dancing around the fire with the travellers, he is wearing a large leather coat. After the police come and go, he's no longer wearing the coat. In the same scene, it shifts from night to day quite quickly, too quickly to be a sunrise.
Continuity mistake: When Edgar takes Duchess and the kittens to be abandoned in the countryside, he is on a motorcycle and sidecar combination. During the trip, the sidecar changes from one side of the bike to the other and back again. Also, when the sidecar separates from the motorcycle while the dogs are chasing Edgar, the wheel on the sidecar switches sides regularly as well.
Continuity mistake: In the scene where Lyle and Ursula slide through the river then over the falls, when they go over the waterfall they are both dry.
Continuity mistake: Delancy's clothing changes from the old school uniform to the new school uniform then back, when checking Blair Willow's room. (00:51:00 - 00:52:00)
Continuity mistake: During the archery constest, in one scene Prince John has a ring on his right paw with no jewel, then all of a sudden the jewel appears. a few scenes later he has three rings on that paw, and later he has no rings at all.
Continuity mistake: When Johnny 5 nearly drives the snack wagon over the edge to where it is hanging, it appears to have miraculously moved right back from the edge, making it look like he never went nearly over in the first place.
Continuity mistake: The band-aid on Jill's doll disappears and reappears several times.
Continuity mistake: When Joe gets injured and he insists the back-up quarterback goes in, he takes his wristband with all the plays on it off, so it can be given to the back-up. When the back-up quarterback is shown running on the field, he does not have it on, but when they show the back-up on the field, he does have the plays wristband on.
Continuity mistake: When Conrad first puts the spider lock in his pocket it is put in his left pocket, but when he takes it out, he takes it out of his right pocket.
Continuity mistake: As Jack Kelly rides the horse near the end of the "Santa Fe" sequence, his hat is waving behind him. When it cuts to a different angle the hat is on his head. Note: This was a specific detail put in by the director, symbolizing the boy's mental transition from New York to Santa Fe. However, it failed and is commonly seen as an editing mistake.
Continuity mistake: When Marty returns to 1985, he goes to his house and gets in his Toyota pick-up. Look closely behind his head when he first gets in the truck, there is no driver-side head rest. But when he picks up Jennifer, when they pull up to the stop sign the head rest is there. (01:45:00)
Continuity mistake: After Spike chases Jean-Claude out of the church, the parents and their kids stand outside. Chuckie is in his father's arms holding his Wa-wa (teddy bear). They go back inside, where Kira gives Chuckie that same missing teddy bear.
Continuity mistake: When he sees Meg in the river of death, he reaches down and touches it. Then, when he jumps in, he makes a dive of at least 50 feet. (01:11:25)
Continuity mistake: When at the poolside of the Bonaventure Hotel, Adam looks at one of the express elevators ascending. Then he turns and runs for the elevators, followed by the blue team. Miraculously, both elevators are now at the bottom floor. (01:40:55)