On the yacht, we see Joe E. Brown's character Osgood Fielding III making a ship to shore phone call using a Hallicrafters Model S-20R which came out in 1939, ten years after the movie took place. Also this radio is only a receiver and not a two-way radio.
Although rim brakes (those on Junior's bicycle) have been in use since the 1890s, the vast majority of early 20th century American bicycles used coaster brakes. In real life, Junior would have been hard-pressed to find a bike with rim brakes.
One of the goons searching for Joe and Jerry assures the other goons that his men have the airports covered. Miami had just one airport at that time, Pan American Field, which consisted of a single hangar and served just one route, Miami-Havana.
The trumpet solo during "I Wanna Be Loved by You" is heard even though the trumpet player behind Daphne and Josephine is not playing her instrument. At one point in the same song, Daphne plays the bass, but the bass isn't heard.
As Sugar sings "I Wanna Be Loved By You" there's an extended shot of her with the drummer, a bit out-of-focus in the rear, and the drummer is clearly "missing" the drum and cymbal by a wide margin with her brushes.
In the funeral-parlor-speakeasy scene, when Joe and Jerry stop playing and make their plans, the bass fiddle part appears to stop on the musical soundtrack as well, but when Jerry begins to hastily pack up his instrument to leave, the bass line can clearly be heard playing again on the songs soundtrack.
Osgood tells Daphne that his mother sent him to Florida when the yearly "George White Scandals" opened. The film is set in February; the "Scandals" never opened earlier than June, and the 1929 revue opened in September.
Mulligan asks for another table not so close to the band and refers to the reserved table. However, we can see in the next shot that the reserved table is right next to the stage and therefore just as close to the band as he is.
When Junior and Sugar return to shore after their night on the Caledonia, they do not tie up the launch to the dock. When Osgood returns to the launch seconds later, he makes no effort to untie it from the dock before he speeds off on it. He should not know that the launch has not been tied up to the dock. If the launch truly had not been tied up to the dock, it would have long drifted out into the open water.
Joe as Junior leaves the hotel by stepping out his window, then walking to his left on the terrace to climb down a pole. When he returns, he climbs over the terrace railing into the window instead of walking on the terrace (after, presumably, climbing up the pole).
In Marilyn Monroe's introductory scene (the platform of the Chicago railroad station), her hairstyle, featuring spit curls, is at least a nod in the direction of the 20s. The next time we see her (on the train, supposedly the same afternoon or evening of departure), her hairstyle is pure late 50s.
After Sugar performs "I Wanna Be Loved by You," we see her back is bare as she turns away from us. When she boards Junior's boat, there is now a transparent strap across her back joining her dress. When she enters the salon moments later, the strap is gone.
When we first see Sugar, we notice the seams of her stockings run a straight line up the middle of her calves. But, when she asks Daphne and Josephine a few minutes later if her seams are straight, they are no longer in a straight line nor up the middle of her calves.
When the bus carrying the band approaches the hotel, there is nobody on the bus but in the next shot, the band exits from the rear door. If people had been on the bus, they would have been easily visible from the side views.
As Daphne dumps her things onto Osgood, his hand is grasping the top of Josephine's saxophone case, the neck of Sugar's ukulele case is pointed away from him while Daphne's purse is stuck between him and Josephine's case. But, when they enter the lobby, Osgood's arm is now under Josephine's case, the neck of Sugar's case is pointed toward him, and Daphne's purse is between Josephine's case and Sugar's case.
Poliakoff's cigarette is one-quarter burned when Sweet Sue and Beinstock leave his office. Moments after Joe and Jerry enter his office, Poliakoff's cigarette is almost down to the stub. When Joe and Jerry are about to leave, Poliakoff's cigarette is half-burned.
While she chops at the ice, Sugar straightens up when she tells Josephine about her weakness for saxophone players. When we cut over her shoulder to see Josephine's reaction, Sugar straightens up again.
When Osgood puts Daphne's shoe on, the luggage on the sidewalk behind him is in a straight line. When we cut back to Osgood, the luggage is no longer in a straight line, and other luggage is stacked on top of it.
In the opening, four hoodlums are riding in the hearse and they hear a police siren behind them. Two of them look out the back window and it is apparent that there is no glass in the window. A second later a bullet smashes the window and, when they look out again, the window is not only broken, but very dirty.
After the back window of the hearse is shot by the police, the two thugs knock out the rest of the window with their guns to shoot back, leaving pieces of glass on the bottom frame. But, the next time we see the hearse, the pieces of glass are gone. When the hearse arrives at the funeral parlor, the pieces of glass are back on the bottom frame.
When Joe and Jerry arrive at Poliakoff's building, Joe's hair is wind-blown with snow in it, and he has stubble on his face. But, when they are in the building, Joe's hair is combed with no snow in it and he's clean-shaven.
At the speakeasy, a lady at a table to Mulligan's left gets up and begins to walk in front of the chorus girls just as we cut to Spats entering. The lady should be now seen in front of Spats, but isn't.
When Spats and his crew go to their table at the speakeasy, the henchman played by Harry Wilson sits at the table directly across from Spats. When Det. Mulligan goes to the table to confront Spats minutes later, Wilson is sitting to the right of Spats.
When Sugar first meets Junior on the beach after tripping over his leg, the ball in background wobbles repeatedly while lying in the sand as if weighted, and looks completely different to the one she picks up after and throws back.
As Daphne and Osgood are going into the hotel, when the camera is outside the hotel Daphne is holding her right wrist up and moving her left arm forwards and backwards. When the camera is inside the hotel, her left wrist is elevated (not as high as the right wrist was) and her right arm is moving.
In the speakeasy as Mulligan packs his cigar, the top of someone's head is in the bottom of the screen. However, when he first sat down at the table, there was no place for anyone to be sitting as he is right next to the stage.
Florida beaches do not have high cliffs. Also, there is a scene where Sugar Kane is sitting on the beach, facing the ocean. She says that the time is 4:00 pm. However, her shadow is clearly being cast behind her. On Miami beaches, this is not possible. Since all of Miami's beaches face east, one's shadow is only cast away from the ocean before noon. On Miami beaches at 4pm, your shadow would lie on the ground in front of you, towards the ocean.
As the police chase the hearse, they pass a "Standard" gas station with the Chevron emblem. The Chevron emblem was used by Standard Oil of California only in the West. In Chicago, Standard stations carried the Torch and Oval emblem of Standard Oil of Indiana.
The PA announcement at the Chicago train station lists the "Florida Limited" making its first stop in Washington and then stops down the East Coast. Trains from Chicago to Florida were routed through Nashville and other mid-South cities.
Early in the movie, Joe talks about the Brooklyn Dodgers, a name not officially used until 1932. From 1914 to 1931 the Brooklyn baseball team was the Robins, not the Dodgers. However, the Dodgers had been an unofficial nickname since 1895, and the World Series program from 1920 even referred to them as the Dodgers instead of the Robins.
The depiction of the St. Valentine's Day Massacre is deliberately inaccurate, to spoof Scarface and other classic gang movies which sensationalized and fictionalized real people (including Al Capone) and events. It's a comedy, not a documentary. To be specific, the shooting took place at mid-morning, not at night. The hitmen did not drive into the garage as shown; they parked outside. They drove a Cadillac, not a Duesenberg Model J as in the movie, and two of the four actual killers were dressed as policemen.
During the chase, the lid of the coffin is leaking fluid from bullet holes which would indicate that the coffin is very full. When the lid is raised, no liquid pours out and only broken bottles are seen.
The card Sugar reads that Joe slipped into the spray of flowers Osgood had delivered to the stage for Daphne tells her that Junior will meet her at the pier after the show. How does Joe know about the pier? And how does he and Sugar know where the pier is?