When Louis is walking past the restaurant in the rain, the scene switches to him a number of times and you can hear the hard rain falling. The first time the camera shows a close up of Louis however, the camera is still inside the restaurant yet the sound of rain falling is heard, drowning out the crowd noises in the restaurant that are heard continuously (other than when Valentine is making his prediction about the Russian wheat crop) when the camera is inside.
When Billy Ray is in the limo, Randolph Duke introduces himself
and Billy Ray asks if the name Randolph is like Randy Jackson of the Jackson 5. Randy was not a member of the Jackson 5. He did not join the group until they became The Jacksons.
When Louis and Penelope are having dinner they have uneaten lobsters on their plates but Coleman is table-preparing Crepe Suzette (a dessert to be served immediately when prepared) and also Louis appears to be drinking brandy which is an after dinner drink (at least the glass is a brandy snifter).
Jim Belushi's character as a party-goer dressed as a gorilla states several times in the film that it's "not even New Years Eve." He is clearly at a New Years Eve party, which would make it New Years Eve, so what the character should be saying is that it's not New Years Day, or that it's not even midnight.
When Mortimer Duke is signing the paychecks, at least one of
the shots is flipped horizontally. At first he signs with his left hand, then his right, then his left again. The part in his hair changes sides as well.
When we first see the Dukes going to work, in the car Mortimer is sitting on the left hand side of the car & Randolph on the right, but when they arrive at work Randolph gets out of the car first on the left.
In the first scene, Louis is going to work, you can see the streets, no snow at all. Later the same day, the Dukes are going to work and as you can see there is plenty of snow. Even later when Billy appears first in the park, plenty of snow.
On Valentine's 'first day on the job,' he enters the Dukes office and the sound of a door closing is heard after he enters, but the chase shot (behind Valentine) reveals the door to still be open, yet in the next shot, from the opposite side of the room, the door is closed.
After Valentine is challenged by the police officers and finally walks away, the camera cuts several times between him and them. The direction towards which he is walking, as shown by the houses in the background, switches back and forth a couple of times.
The Dukes park their limo on Locust Street heading west right before Billy Ray appears. Locust Street is one way heading east and all other times in the movie we see the cars heading east on Locust Street.
After Randolph states it will take more than just losing his job to drive Winthorpe to criminal activity, and listing the other misfortunes that may be required, it is Mortimer that adds to surround him with the "wrong sort of people" to push him over the line. However, Mortimer doesn't believe that environment influences behavior, and states so with his race horse analogy (showing a lack of understanding since race horses won't succeed without training, i.e. environment) so why would HE be making this suggestion? It is understandable when he puts up the front for Valentine, so as not to bias the "experiment", but it wasn't necessary here since they hadn't started, yet.
In the park after the 2 cops expose Billy Ray, the cop on the right is standing with his legs slightly apart facing the camera. The shot from behind shows him standing with his hips to the right, one leg behind the other.
In the interior exchange in the police station between Winthorpe and Penelope - immediately after Winthorpe is released on bail - his blackened left eye is open and blinking; in the scenes that follow, he forces it closed, as if swollen shut.
When Winthorpe is in the cab and Valentine is in the limo and they see each other, the street they are on, outside Independence Hall, is two-way traffic. This was only done for the movie. In real life, this is a one way street heading east. You can see the white lines on the street dividing the travel lanes, rather than a double yellow line which would be needed for it to be denoted as a two-way street.
On the train from Washington to New York, the sound of the train passing railroad crossings is heard several times. Due to the electrification of the Amtrak Northeast Corridor line, nearly all grade crossings have been removed.
At the Christmas party when Winthorpe jumps on the table waving the gun, the clocks show that it is 1905 in Los Angeles, 2205 in Philadelphia and 0205 in London. London should read 0305. London is five hours, not four, ahead of Philadelphia, regardless whether in Daylight Savings Time (British Summer Time) or in Standard Time.
The time shown for Hong Kong in the back of the Dukes' car is 6:51, which is 13 hours ahead of Philadelphia. Since it's an analog clock the possible local times are 5:51 am or 5:51 pm. Either one of those times it would be dark during the Winter in Philly.
When Billy ray is released from jail, Randolph says that they are "the ones that bailed you out." Later, during the conversation in the limo, Billy Ray asks, ""What about the police and the payroll?" The Dukes state that they have had the charges dropped. If the charges were dropped, then there would have been no need for bail. Bail is a conditional release/promise to appear in a future court date; which would not be necessary with dropped criminal charges.
Winthorpe's car, a Mercedes Benz 600 Grosser - is unique in that it features a complex hydraulic system that runs everything from the windows to the suspension. The car would need time to run and generate enough hydraulic pressure for the suspension to raise the car to proper operating height. It would not be possible for Coleman to just start the car and drive to work as is done in the beginning of the movie.
The baggage car show at the end of the train leaving Washington appears to be a passenger Amfleet car with the windows covered and red/blue stripes painted over the windows - there's no such thing as an Amfleet baggage car.
When shown on television, the scene where Dan Akroyd is choking Eddie Murphy, the viewer can clearly see Dan's hands when it shows the view from Eddie's perspective, which is impossible if seen from the viewpoint of the person being choked.
When Billy Ray comes out of jail, after of being bailed out, the Dukes confirm that they bailed out Billy Ray before he gets in to the car. After they get in the car they say, "We had the charges dropped". If the Dukes dropped the charges there would be no need to pay the bail.
The Dukes ruin Winthorpe by framing him for robbery and possession of PCP. He's told he faces 3 to 5 years in prison. His girlfriend bails him out of jail and later he meets his friends at a country club asking to borrow money for his defense fund to fight the charges. Yet after this, there is no other mention made of his legal troubles and the whole plot point is dropped. It's possible the Dukes made the whole thing go away (as they did with Valentine) but it's never mentioned.
At the Christmas party, Louis steals food, plants drugs, and threatens everyone with a gun including a security guard. Yet he is allowed to casually walk out of the building unimpeded with no one bothering even call the cops.
During early scenes in the movie there's a fair amount of snow on the ground, but later scenes show a completely dry and snow-free Philadelphia. In fact, one overhead shot of Constitution Hall and the surrounding park shows green grass and leaves on the trees - highly unlikely in Philadelphia at Christmas time.
In the large room when framing Louis, everyone is instructed to place the contents of the jacket pocket of the person to their right on the table. The people lining the walls have no such tables. The people on the right end have nobody emptying their left pockets.
The road in which Winthorpe and Valentine meet in the taxi and limousine is delineated by a white line. Yellow lines are always used to delineate opposing lanes, while solid white lines delineate the right edge of a traffic lane, and sometimes lanes going in the same direction.
When the members of the club are asked to dig inside the pocket of the man to their right and to put the content in front of them, the row of members in the back of the room do not have any table or any support on where to put said content, as they are only sitting on chairs.
After getting off the bus, there is the sound of peeing as the dog lifts its leg near Louis but there is clearly no liquid coming out. After the dog walks away his pants are still dry and there is no puddle on the ground.
During the frenzied trading floor scene, just after the announcement of the Secretary of Agriculture saying,
"Ladies and Gentlemen, the Orange Crop Estimates for the next year..."
The very next frame shows Dan Akroyd with his order pads facing the camera, completely covered in scribbles. No note taking or information on who he bought or sold to.