(at around 48 mins) Spade doesn't wear rings or a watch throughout the movie except for one scene. At one point he walks into his office wearing a wedding band on his left hand, another large ring on his right hand and an expensive-looking wristwatch. He sits down to have a quick chat with his secretary where the rings and watch are in plain view. He then walks through a doorway into his inner office and the rings and watch are gone.
When Spade backslaps Cairo, and Peter Lorre's head snaps to the left, he's wearing a polka dot bow tie, but when his head snaps back to the right, his cravat has become striped.
(at around 57 mins) When Spade pulls Wilmer's overcoat over him going towards Gutman's apartment, he pulls out two pistols. Wilmer has his hands inside of his coat's outer pockets, however, and the viewer doesn't see Spade's hands going into two upper inside pockets.
(at around 51 mins) When Sam first goes to see Gutman in 12C, as he walks down the corridor, directly in front of him are a chair, a table with flowers on it and a silhouette of a diamond framed window, and the flowers on the wall. When he leaves, there are two chairs on either side of the table, but the diamond frame silhouette is not there.
(at around 1h 27 mins) When Sam first puts the Falcon on the table Gutman is smoking a cigar. When he begins to scratch the Falcon there is no cigar in sight.
The opening crawl begins, "In 1539, the Knight Templars[sic] of Malta, paid tribute to Charles V of Spain, by sending him a Golden Falcon..." This confuses two different religious orders of knights, both founded in Jerusalem. The Knights Hospitallers of the Order of St. John of Jerusalem, known as the Order of St. John for short, have existed since 1048; they were in fact based in Malta from 1530 to 1798 and hence were also called the Knights of Malta. On the other hand, the Knights of the Temple of Solomon, also called the Knights Templar or just Templars, were founded in 1119 and became the sworn enemies of the first order; this latter group was disbanded by 1312, after King Philip IV of France had declared them heretics so that he could confiscate their wealth.
The opening crawl tells a story about "Charles V of Spain" in 1539. This king was Charles I of Spain; Charles V was his title as Holy Roman Emperor.
(at around 8 mins) When Spade and Tom Polhaus are discussing the murder of Archer, Polhaus says the murder weapon is a "Webley". Spade then goes on to describe the weapon as a "Webley-Forsby (sic), .45 Automatic, 8-shot". The manufacturer was Webley-Fosbery, though Sam may have just mispronounced it, but the similarity to "Thursby" is striking. What is most definitely wrong is the Webley-Fosbery Automatic Revolver was chambered in two calibers, .455 Webley MK II (not .45, a minor discrepancy) and .38 ACP. The .455 had only a six-shot capacity, and the .38 caliber was the 8-shot variant. The .455 Webley MK II was an unusual cartridge and would have been quite hard to find after 1915, the end of production for the pistol. The .38 ACP was more common and is still available today. In the Dashiell Hammett book, the weapon is correctly referred to as a .38 caliber, 8-shot.
The opening crawl states the Falcon was created by the 'Knights Templar of Malta'. The Knights Templar and the Knights of Malta were two different groups and sworn enemies.
When Archer first enters Sam's office in the opening scene, he opens the door and is smoking a cigarette. Archer quickly removes something from his mouth nonchalantly with his right hand, he immediately puts his hand down to his side and then discards it on the floor hoping it wasn't noticed. This second item is a toothpick. When he comes into the room, he has 2 distinct items in his mouth, one a cigarette, the other the toothpick he tosses to the floor.
(at around 8 mins) Spade refers to the gun as an automatic, yet he is shown a revolver. The gun shown is a Webley-Fosbery automatic. This was a revolver that used the recoil of the shot to turn the cylinder and re-cock the weapon. It was very well made, but susceptible to dirt and fouling and so, as Spade said, "They don't make 'em anymore". However, it was made in two versions, a six-shot .455 and an eight-shot .38 ACP, so it can't actually be an eight-shot .45 as Spade says it is.
(at around 8 mins) When Spade is talking to Det. Tom Polhaus about the Webley, the sound stage ceiling can be clearly seen above the tops of the buildings.
San Francisco firefighters have Los Angeles Fire Department uniforms.
Although the film is set in San Francisco, on the fire ship that was putting out the fire on the La Paloma a life saver hanging on the outside wall reads 'L.A. CITY NO 2.
At one point near the beginning, the sun casts an image on the floor of a window bearing the Spade and Archer text. The angle of the light does not correspond to either of the windows and is also at an odd angle.
(at around 26 mins) When Sam clobbers Cairo, he falls unconscious on the sofa. Cairo can be seen blinking pretty obviously.
The second time Sidney Greenstreet says the word "falcon", he pronounces the first syllable to rhyme with "pal" or "shall". All the rest of the times he says the word, he pronounces it to rhyme with "pall" or "shawl".
(at around 25 mins) Joel Cairo's passport refers to Lepanto. This name is an Italian name and hasn't been used since the middle ages; the current name (and that in use since Cairo's birth) is Naupactus.
(at around 47 mins) When Effie is on the phone with Iva, she is heard to say, "No, not yet", but her mouth is closed.
(at around 1h 7 mins) Shadows are visible when Captain Jacoby stumbles into Spade's office and falls on the couch.
When looking to newspaper for ship arrivals, it seems that small piece of paper has been glued there.
(at around 1h 6 mins) "L.A.F.D." (Los Angeles Fire Department) appears on the firefighters' helmets, and "L.A. City" on the La Paloma's life preserver. The film is set in San Francisco.
Los Angeles Fire Department appears on firefighters hats though story is based in San Francisco.
(at around 2 mins) Early in the film, out the window of Sam's office, the Bay Bridge can be seen. In another angle, a domed building can be seen - either SF City Hall or the monument at Presidio, neither of which would be visible from Sam Spade's office.
Sam Spade never verified whether the Maltese falcon was genuine or not.
The odds of the Maltese falcon magically showing up is microscopic.
(at around 57 mins) When Spade and Wilmer are walking down the hall toward Gutman's apartment, the shadow of the microphone boom passes across Wilmer's coat.
If the statuette were genuine, Gutman would not be trying to scrape the enamel from the visible surface of the falcon, but from the bottom. Otherwise, the knife marks would damage the piece and would seriously degrade its value.
Joe tells Sam that he's staying at the Hotel Belvedere, room 635. Later he enters the hotel goes to the desk and asks for the key to room 603.
(at around 54 mins) In their first meeting, Spade tells Gutman that he has until 5 o'clock to make up his mind. Later, when Wilmer lets Spade know that Gutman is ready to talk, Spade says, "I didn't expect you until 5:25", which would have been twenty-five minutes after the deadline had passed. (In the novel, the deadline is 5:30.)
The crawl at the beginning of the movie refers to the falcon as being "encrusted from beak to claw with rarest jewels". Yet when it is finally seen, the falcon's surfaces are all smooth. Even with the black enamel coating to disguise it, it seems the rough texture of the jewels below the enamel should be apparent.
When Spade calls his secretary Effie to ask her to make death notification to partner's wife, he calls her Dorothy instead of Effie.