Continuity: The dog and the book briefly change between Kurtz' two hands when he is being shown where Lime was hit by a truck.
Continuity: The position of Anna's neck ribbon when she and Holly first talk.
Continuity: Three cats were used for Harry Lime's only loved cat. But all three cats had different sizes and colors.
Continuity: After the funeral for Harry in the Zentralfriedhof Anna goes into the straight alley. We see her shadow on the right side on the screen
Revealing mistakes: In the two separate back projection shots of Calloway, Martens and Paine, supposedly traveling in a jeep at night in Vienna, a double-decker London bus can be seen in background.
Continuity: The policemen who come to arrest Anna change between shots. In dialogue scenes the British policeman is played by Geoffrey Keen. In shots of the Jeep driving to the apartment, and in long shots, a different actor is used.
Continuity: Harry Lime's sewer scenes were shot in two locations (in UK studios and on location in Vienna's sewer). In the Vienna sewer location scenes you can see Harry's breath.In the sewer shots done in UK you cannot see his breath.
Audio/visual unsynchronized: After Calloway has shown Martins the evidence against Lime, Calloway picks up the phone. We hear his line, "Get me Police headquarters," but we don't see his lips move.
Continuity: In the sewer before putting fingers through grate, Harry Lime holds the stair's supporting pole with his right hand, but the gun should be in his hand, as displayed before and after this shot.
Errors made by characters (possibly deliberate errors by the filmmakers): The line about the cuckoo clock being Switzerland's only contribution to culture is factually incorrect: the cuckoo clock comes from the Black Forest, across the border in S.W. Germany.
Continuity: When Calloway and the police stand waiting for Harry to arrive at the station, an elderly balloon man tries to sell them a balloon. His balloons have designs printed on them. Calloway has the Seargant buy one to get rid of the old man but the balloon has no printing on it as the shot of the police was filmed later in London.
Revealing mistakes: When Martins arrives at the funeral and ask Major Calloway whose funeral this is, a black tombstone is seen behind Martins. When he walks toward the grave and stands by Anna, the same tombstone is seen behind her. This occurred because those scenes were both filmed, not on location, but later in Shepperton studio where only a handful fake tombstones were available.