Continuity mistake: When Melinda Dillon breaks the lamp, it is broken into many pieces, but when Darren McGavin is gluing it back together it is now in much fewer and bigger broken pieces. Obviously different broken lamps were used.
Visible crew/equipment: After Mortimer's comment that Billy Ray has probably been stealing since he could crawl, when it cuts to the two officers opening the squad doors to place Billy Ray at the back of the vehicle, the barndoor set lighting is visible over the squad car at the top right corner of the screen. (00:18:25)
Other mistake: Towards the end of the movie, when Superman drops Gus off at the coal mine, Gus begins talking with the coal miners about him and Superman. He then rips open his shirt (as if he had a Superman costume on underneath). How did Gus know that Clark Kent tore his shirt like that in order to change into Superman, or keeps his suit under his clothes at all? The only people who know this fact are the ones who have seen the transformation from Clark to Superman, i.e. the audience.
Revealing mistake: In the early part of the film, Beverly D'Angelo and Chevy Chase check into the hotel/motel. She goes in to take a shower but he barges in. If you look real closely, she is wearing underpants and is not nude although she is taking a shower.
Continuity mistake: In the movie's final moments when Tom Cruise is buying back all his household items, the lady in the cargo bay says "that's everything," except for the crystal egg she throws out into the yard for Tom to catch. You can clearly see many more items left in the truck. But when the truck pulls away seconds later, nothing is left in the cargo bay except our villain sitting on a chair. Where did everything else go?
Continuity mistake: During The Miracle of Birth Part 1, when the guy goes into the operating room, the girl puts the gown on the first doctor. It's barely on, but, in the next, wider shot of him, it's completely on and she's tying the back together. (00:04:30)
Continuity mistake: When Jack kicks the TV it falls backwards, and the screen has snow on it. However, when the repair technician comes in, the screen is broken.
Continuity mistake: When the brunette is in the shower and that boy shows up he is wearing brown pants, but when you see the clothes lying on the carpet while they are in bed together, the pants are blue jeans. (00:59:00)
Continuity mistake: At the end of Porky's, you see Mickey Jarvis on crutches and covered in bandages after getting beaten up by Porky. In the beginning of Porky's 2: The Next Day, Mickey has miraculously healed. He jumps out of his truck to catch up with the other guys, no crutches or bandages and he is walking fine.
Continuity mistake: Mention is made that Pamela owns the brewery because she has just turned 21. During the scene with the video game, she says her birthday was October 21, 1959. Later, the lawyer for Bob and Doug establishes the movie's timeframe by mentioning her kidnapping on October 10, 1983, which would make Pamela almost 24 years old instead.
Factual error: When we first see Fatima Blush, she is waterskiing. She is doing several stunts, which are only possible with one ski, the most notable being skiing backwards with one foot in the air. However, when she releases the tow rope and skis up the ramp into James Bond's arms, she is on two skis. (00:45:55)
Continuity mistake: When Cheech gets off the stage in the beginning of the final show, you can see the spotlights on him when he is walking towards the curtains. When it cuts to a wide shot Cheech is gone and the spotlight is off. (01:04:25)
Factual error: Shirley MacLaine and Jack Nicholson both live in River Oaks (very ritzy neighborhood in Houston) and are traveling to Brennans restaurant in downtown Houston maybe 5-10 miles away - but they go by way of Galveston which is about 45 miles south of Houston - which needless to say is way way out of the way... (00:50:40)
Visible crew/equipment: During the scene where Nick and Sam come upon Richard having a midnight snack in the kitchen you can see a small bright whitish reflection of some kind of equipment in the top left (our left) kitchen window, down in the lower right corner. There is no character movement or other scene related explanation for this reflection. It moves and fades during the scene, most dramatically at the end of the scene. (00:37:20)
Continuity mistake: During the scene where Rita is riding a bus, between shots the view outside changes from south quays, dame street, and back to the docklands, even though these places are several minutes bus ride away from one another and in different order.
Continuity mistake: In the diner, Walter Matthau has nearly finished his piece of toast, and then it gets bigger.
Deliberate mistake: When Cletus is driving the Trans Am as the bandit, it shows him driving to the left and waving at a group of girls. The close up of him driving must be reversed because it looks like the Trans Am is now a right-hand drive. (00:26:45)
Factual error: Part of the movie takes place in Vienna, Austria. Although the number plates of the cars are like those in Austria at that time, neither the road markings nor the street car which can be seen when both Steve Martin and Kathleen Turner are "climbing" outside their hotel look like those in Vienna.
Factual error: The caption says "twenty years later" before the main part of the movie starts. Now judging by the dates we've seen on-screen so far that would be in the reign of William and Mary, not Queen Anne.
Continuity mistake: Jenny Seagrove takes Peter Capaldi to see Grey seals only it's clearly stock footage of sealions, totally different animals not found in Scotland.