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 he first enters his office, Archer is smoking a cigarette with his left hand, and appears to be holding a match in his lowered right hand. He seems to have been caught holding the match he used to light the cigarette before entering the scene, and disposes of it by casually dropping it to the floor.
When Dundy and Polhaus are in the Spade's house, Spade serves a drink to them. When he begins to serve, Dundy is standing and Polhaus sitting. Then Polhaus stands up in the right side of Spade. Next shot he is in front of Spade.
When Sam first goes to see Gutman in 12C, as he walks down the corridor we can see that directly in front of him is a chair, a table with flowers on and a silhouette of a diamond framed window and the flowers on the wall, but when he leaves we can see two chairs either side of the table and the diamond frame silhouette is not there.
In their first meeting, Spade tells Gutman that he has until 5:00 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).
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.
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.
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.
After Gutman discovers the Maltese Falcon is a fake and shakes off the shock, he puts the statue upright. A close-up of the bird and Gutman's hands shows a knife in his right hand, though in the previous long shot his hand was empty.
When Wilmer is overpowered in the last scene in Spade's apartment, he's placed on the lounge with both arms at his side. After a momentary cutaway shot to Brigid's face, he's shown with both arms over his head.
When the La Paloma burns, a sign reading "Port of Los Angeles" is seen over a door leading onto a wharf, and "Los Angeles Fire Department" appears on the firefighters' hats. The film is set in San Francisco.
At the very end, as O'Shaughnessy and Dundy are leaving in the elevator, the visual effect of the elevator going down is accomplished by lowering a dark screen in front of the backlit actors. Very nice, except that you can clearly see that both silhouetted actors remain standing motionless at floor level as the screen drops.