Continuity mistake: When there is an overhead shot inside of Winthrop's house when Billy Ray is giving a party, look down on the right hand side - a lady in a black dress is passed out, with her legs draped over a guy's lap. The next scene is a close up, and she's now lying against his chest (head first), then the next scene, she's back lying at the other end of the couch with her legs draped over his lap.
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)
Continuity mistake: When Louie is released from jail his hair is sticking up all wild, then it's flat, then it's all wild again. (00:47:25)
Continuity mistake: At the start when Billy Ray (Murphy) is backing away from the cops after he was pretending to be a cripple, he passes the Heritage club. In front of the steps of the Club, he turns to face the other way. The camera changes angle as Billy Ray completes his 180 turn, but he is now no longer at the steps of the Heritage club, but about 10 feet beyond it, nearer to where the other cops in the patrol car come out of the alley way. (00:15:50)
Continuity mistake: When Valentine is in the limousine with Mortimer and Randolph, he has a bunch of cigars in his left hand. The position of those cigars change from shot-to-shot. One is hanging down very low when looked at from Randolph's side of the car, then immediately it is even with the others when seen from Mortimer's side. (00:28:00)
Factual error: The Amtrak Metroliner has open passenger coaches, not the European-style compartments as seen in the movie. (01:30:45)
Continuity mistake: When Valentine (Murphy) and Winthorpe (Aykroyd) are at Winthorpe's house at the end of the movie. Winthorpe is on the floor cleaning his gun. In the next shot Ophelia (Jamie Lee Curtis) points out Beeks on TV and Valentine and Winthorpe jump up from the couch when Winthorpe should have been and was on the floor. (01:25:30)
Continuity mistake: A woman is seen dancing next to a portrait on the wall, and is immediately afterwards sitting on a couch next to Billy Ray. (00:41:40)
Deliberate mistake: Eddie Murphy is giving his first party and tells everyone to leave. The valet holds all the coats in a perfect pile for the people to grab them as they leave. Although everyone rushes out of the party, it's very strange that the first person to leave takes the first coat, the second person the second coat and so on until the very last guest. No one stops to check if the coat they're taking is really theirs. (I guess it was shot this way to keep the good pace of the sequence). (00:43:55)
Other mistake: At the start of the movie it shows the house at front view and the sky is very very grey, it looks like it's about to rain, then after a short scene inside the house it goes back outside and the sky is clearly blue with not a cloud in sight. (00:12:00)
Factual error: When Beeks is locked in the cage with the gorilla, it reacts in an overtly aggressive and sexual manner. First, gorillas are shy and gentle creatures. The male gorilla would be scared of him, not the other way around. Second, gorillas identify each other by their smell, and the smell of a female in heat is very specific. Beeks would smell like a horsehair rug and the male gorilla wouldn't be the slightest bit interested.
Continuity mistake: During the final trading scene, both Dan and Eddie (along with most of the other traders) have green badges. As the medics are wheeling out one of the Dukes after his heart attack, Dan and Eddie's name badges change to grey. And in no way is that due to lighting or camera angle.