Continuity: The frozen daiquiri in the cocktail lounge melts, reforms, and melts again.
Continuity: A week-old strand of spaghetti on Baxter's tennis racquet is still soft and pliable.
Continuity: Fran's hair keeps shifting and changing during the gin rummy game.
Continuity: Baxter gives Fran coffee to drink. The coffee is freshly made and so it's boiling hot, but she drinks it quickly, as if it had been sitting around for some time.
Continuity: After Bud finds out that Ms. Kubelik was with Mr. Sheldrake, he leaves wearing his new hat, leaving his old hat behind. Later that night when he arrives home with the woman from the bar, his old hat is on the hat rack on the wall.
Errors in geography: During the opening pan of the New York skyline with the United Nations Building in the foreground, the shot is actually a "mirror-image" of the actual scene.
Errors made by characters (possibly deliberate errors by the filmmakers): At the very end of the film, Baxter and Fran sit down to play a game of Gin. This game is played with 10 cards dealt to each player, but Baxter deals at least 13 cards to both Fran and himself before the picture finally fades out.
Factual errors: Prior to the introduction of microwaves years later, C.C. Baxter could never have popped a frozen TV dinner in an oven, cooked it and sat down to dinner within the short time span he does in the movie - the space of a few minutes.
Errors made by characters (possibly deliberate errors by the filmmakers): When telling the story of his attempted suicide, C. C. Baxter pantomimes loading a revolver, even though he has specified (and we later see) that the gun he used was an automatic.
Crew or equipment visible: During the scene in which Fran cries in front of the mantle, you can clearly someone reflected in the TV screen sitting and watching the scene play out.
Boom mic visible: (Widescreen version only) The shadow of a boom mic is visible in the upper left portion of the screen as C. C. Baxter is rushing to open his apartment door after being alerted to an odor of gas by his landlady.
Continuity: Baxter's pajamas are inconsistent when he is first kicked out of his apartment.
Continuity: The shaving cream on Baxter's faces changes between the bathroom and bedroom.
Errors made by characters (possibly deliberate errors by the filmmakers): When Sheldrake calls the Personnel Department to get Baxter's home number after Fran's suicide incident, he says Baxter is in "ordinary premium accounting" even though Sheldrake had already promoted Baxter to a junior executive position.
Revealing mistakes: The layout of Baxter's apartment makes no sense, especially in the context of Dr. Dreyfus's apartment. Dreyfus lives next to Baxter, which means their walls should be adjoining the full length of both flats. But from inside Baxter's living room one can see windows in both his kitchen and bedroom facing directly where the Dreyfus apartment should be (and there would likely be a window in the bathroom between the kitchen and bedroom). Dreyfus's apartment would have to veer immediately off to the extreme right when you enter it and be no more than a couple of inches wide in order to allow the kind of set-up seen in Baxter's apartment - clearly unrealistic, if not downright impossible.
Revealing mistakes: In the scene where Mr. Baxter "Buddy Boy" puts the message on the phonograph for when Mr. Dobisch is coming over it reads 'NOT TO LOUD'. To be grammatically correct it should have read 'NOT TOO LOUD'.
Revealing mistakes: Fran buys a record album recorded by the small combo that performs in the Chinese restaurant she patronizes but when the record is played in Baxter's apartment, the tunes are lush orchestral arrangements, nothing like the lounge music heard in the café.
Errors made by characters (possibly deliberate errors by the filmmakers): After her suicide attempt, Fran does not know she is at Baxter place but his name must have been on the sleeping pills jar she gazed at for more than a minute.