Revealing mistake: While Akeem is getting his hair cut, you can see the reflection of the white character he plays in the mirror. It is quite obviously a stand-in, with a fatter face and different glasses. (00:33:45)
Revealing mistake: When they are at the Nutmar camp in the mountains, Val Kilmer tells Willow "Get on that shield!" but when they go over a 6, 7, 8 foot drop when they are sledding down the snow, you can clearly see runners on the shield.
Revealing mistake: When they show Heather Chandler in her casket in the funeral scene and everyone is praying, she's clearly breathing.
Revealing mistake: When Charlie and Daisy get the flat and have to hitch-hike, and Daisy takes off her shoes to run to the car that has stopped, the bottoms of her feet are already filthy (presumably from having to do the scene over and over).
Revealing mistake: Near the end of the film, a B-52 seen flying across the screen. The bracket holding up the model is visible.
Revealing mistake: Apparently filmed inside an old warehouse, heavy masonry walls can be observed during some scenes inside what is supposed to be a spaceship.
Revealing mistake: When the window slams on Nordberg's hand it is that the window stops right above his hand. When he pulls his hand out the window doesn't go all the way down and a wooden cube is visible on the edge of the window stopping it from closing. (00:06:50)
Revealing mistake: At the end of the movie when Josh and his friend are walking down the street, a lady crosses the street in front of them. Look closely to the left of the screen. The lady is obviously behind the tree waiting for her cue because she is not seen walking toward the tree before crossing the street. (02:06:40)
Revealing mistake: When the projector blows up in Alfredo's face, it's quite obvious to see the stuntman replacement and his protective clothing as he falls to the floor. (00:54:30)
Revealing mistake: The "Great Train Robbery" actually took place on a two-track railway near Cheddington - the West Coast Main Line. However, the filming took place on the Great Central Railway steam line near Loughborough, which only had one track at that time. They laid a second track for the filming, but omitted to cut down a large tree at the end of the rails, which would block the path of a train. This is blindingly obvious, especially as they show this "atmosphere shot" twice. The tree is still there the second time.
Revealing mistake: In the scene when the aliens first enter Valerie's house, Mac and Zeebo find the fish tank and eat one fish each. The shot turns to Valerie's stunned reaction then back to the aliens, who are smiling widely, pleased with their stunt. If you look at Mac's teeth, you can see they are bright white up to his first molar, which is a give-away at his fake white fronts.
Revealing mistake: The palm trees next to the building Arthur came out were not real trees. One is flush against the front wall of the building and another is in a nearby corner. The palm tree in front looked completely flat - like a large piece of cardboard or maybe painted on the wall. Palm trees should be at least 30' away from a structure as well as outdoor pipes, buried lines, etc. They grow a big central root below the trunk and MANY thin roots running horizontal close to the surface - some may be exposed. (00:05:51)