After filming had ended, Cary Grant kept the famous UNICA key. A few years later he gave the key to his great friend and co-star Ingrid Bergman, saying that the key had given him luck and hoped it would do the same for her. Many years later, at a tribute to director Sir Alfred Hitchcock, Bergman went off-script and presented the key to him, to his surprise and delight.

Sir Alfred Hitchcock got the shot where Ingrid Bergman is in the background and the coffee cup is in the foreground, with both in focus, by using a giant coffee cup placed farther away than it appears.

Director Sir Alfred Hitchcock and screenwriter Ben Hecht consulted Nobel Prize winner Dr. Robert Millikan on how to make an atomic bomb. He refused to answer, but confirmed that the principal ingredient, uranium, could fit in a wine bottle.

Sir Alfred Hitchcock claimed that the F.B.I. had him under surveillance for three months because this movie dealt with uranium. During production in early 1945, the use for uranium ore was not common knowledge due to secrecy. But, after the dropping of the atomic bomb on Hiroshima on August 6, 1945, and the release of details of the Manhattan Project, removed any doubts about its use.

Leopoldine Konstantin played the mother of Claude Rains, but in real life, she was only four years older than he.

Continuity

When Devlin and Alicia are having a drink at an outside table in a busy cafe, the same portion of background film was used in two separate parts of their dialogue (a man walks away from the camera, then a waiter approaches a distant table and starts to put down some drinks from his tray).

When Ingrid Bergman's character is slowly realizing that she is being poisoned, the liquid in her cup changes. She seems to drink it all; but in the next moment, the cup is full.

Did Hitch goof? At the dinner which Alicia Huberman (Ingrid Bergman) attends with all the I.G. Farben baddies, there seems to be an uncharacteristic slip-up for the usually meticulous and detailed oriented Hitchcock. The labeled bottles of wine "(Volnay) Cailleret Bouchard" that Emille Hubka (E.A. Krumschmidt) is visibly disturbed about, bears totally NO resemblance to the later bottles of "Pommard," those down in the Sebastian wine cellar, where some specific ones contain the radioactive ore samples. For one thing, the earlier bottles have no separate vintage labels as do the 1934 bottles in question, and, even the bottle shape is wrong.

At the coffee shop in Rio, Devlin's hands are repeatedly folded/unfolded between shots.

When Alicia and Devlin are first seen sitting at an outdoor cafe in Rio, she mentions that she's been sober for eight days. Since she was drunk at the party where she met Devlin, and they left for Rio one day later, this means they've been in Rio at least a week. But in one of the next scenes, Captain Prescott says Alicia just arrived in Rio "the other day" and he hasn't met her yet.



Revealing mistakes

At about 1:22, Ingrid Bergman is suddenly stricken by the poison. In a long shot as she and Rains walk away from their meal on the terrace, Bergman is obviously taller than Rains. In the next shot, the camera is closer and they are more equal in height, but as they walk away from the camera even with her head bowed Bergman obviously becomes taller than Rains again.

When Alicia and Devlin are flying to South America, the movement of the clouds makes it appear that the plane is flying backwards.

Alicia and Devlin's shadows can be seen "over" the background plates during the drunk driving scene and the balcony scene.



Audio/visual unsynchronized

When the motorcycle officer is approaching Alicia's car, the rear-view mirror has the same image as we see behind Devlin and Alicia, not the reverse.

When Devlin visits Alicia sick in bed, she says, "They are poisoning me," and continues to speak, but her lips do not move.

In the distant shot of Sebastian sitting in his mother's bedroom, the first time he calls: "Mother," his lips are not moving.



Crew or equipment visible

When Devlin and Alicia go to find Sebastian riding horses, there is a quick two-second shot of all four characters next to each other on horses and two arms are visible walking the horses of Sebastian and the woman with whom he is riding.

In the scene when Alicia and Sebastian were having coffee (1:20), there is a hair at the bottom of the screen - the gate wasn't checked.



Errors in geography

It is quite improbable that there are fireplaces in apartments in Rio De Janeiro.

Early in the movie, an intoxicated Alicia Huberman asks to go driving with T.R. Devlin. They are then seen driving in a 1941 Cadillac Series 62 Deluxe convertible in Miami Florida (top down). Current year of the movie is 1946. The 1941 Cadillac Series 62 Convertible is a rare model with only 3100 units built. Later in the movie, Alicia Huberman and T.R. Devlin fly to Brazil. Once in Rio de Janeiro, Alicia and T.R. are again seen driving in a 1941 Cadillac Series 62 Convertible (top up) which would have been extremely rare in Brazil. Less than 500 were built for export. The same car is used in both scenes. This would have been impossible in real life as the flight would have taken hours to Rio where shipping the car would have taken weeks. Both Rio scenes and Miami scenes were shot in either country using the same car.



Plot holes

At the end of the movie when Devlin doesn't let Alex in the car as he takes Alicia to the hospital, it is suggested that he will be killed for marrying an American agent. Why wouldn't they bring him along and try to get intelligence from him with the threat of death if he goes back with his associates. His knowledge would be invaluable to the intelligence organization. It seems illogical to pass on such an opportunity.



Boom mic visible

When Alicia and Devlin are riding their horses (and about to meet up with Sebastian), the shadow of the microphone boom can clearly be seen as it passes over Alicia's face when they ride out from under the trees.



Character error

When drunken Alicia is struggling with Devlin in her car at the beginning of the movie, after he causes her to pass out, Ingrid Bergman can be seen sliding over in the car seat to make room for Cary Grant.

All the German characters are all the time speaking English to each other instead of German.