Continuity mistake: In the scene when Jamie Lee Curtis brings Dan Aykroyd home, you can visibly see she is wearing pantyhose. However, just a few second later, inside the apartment, she takes off her dress and is only wearing panties.
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.
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.
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.
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.
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.
Factual error: The Amtrak Metroliner has open passenger coaches, not the European-style compartments as seen in the movie.
Continuity mistake: In the very last scene, Eddy Murphy is on the beach, and Dan Ackroyd, with Jamie Lee Curtis is on a yacht. They exchange what are now classic lines: "Looking good, Billy Ray!" "Feeling good, Louis!" But the yacht is way off shore. There's no way they could hear each other at such a distance, even at the loud voice that we as viewers hear.
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.
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).
Continuity mistake: When Dan Aykroyd tries to strangle Eddie Murphy and the shot changes to a close-up of Dan, you can see that he is not holding on to Eddie's throat but just holds them in the air.
Continuity mistake: In the scene at which Dan Aykroyd first joins his employers at the gentleman's club, Don Ameche is shown mirror image. This same scene is repeated at the very end during Ameche's credit.