When Barry and Eileen are sitting at the table they get the note that Barry has been waiting for which reads "S.S.Pelican Docked at Half-Moon Bay -Gene". The note is typed. When the spies retrieve the note from Eileen's bag and put the torn note together it is handwritten.
When Barry is cornered by the enemy agents in the back of a cab, exterior shots show extensive fog, but out the rear widow of the cab, the weather is perfectly clear, save for a few puffs of fog blown in at the end of the scene.
The film opens with an establishing shot of the San Francisco Bay Bridge, then shows Eileen Carr (Nina Foch) standing on a bridge walkway and being accosted by a policeman who asks if she's there to kill herself. The Bay Bridge has no walkway and is not known as a suicide site; scenarist Aubrey Wisberg probably had it confused with the Golden Gate Bridge, which does have a walkway and is famous as a suicide bridge.
Undercover secret agents on a mission to not carry a badge with them to identify them as such - as when Barry flashes a badge emblazoned with "Federal Agent" to the cop on the bridge.
Eileen states she was in the service in WWII and was on a hospital ship sunk by enemy bombs. There was no U.S. hospital ship sunk in WWII. Perhaps since this picture was filmed in December 1943 the screen writer anticipated this would happen.
In many of the "fog" scenes, the fog has obviously been put in the shot in post, as said fog follows the camera movements.
Barry holds a small lens with "Hail Japan" written on it. His hand is not steady, but the image projected onto the storefront window does not move in the slightest.
The film shot of the bridge at the beginning of the movie and the end is the same. The headlights moving across the bridge are at the same point in the film footage.
In both Eileen's dream and in the later real life scene, she looks at her watch, which reads 10:25, yet later Barry is trying to find the name of a ship that passed under the bridge at midnight, an hour and 35 minutes later.
The listening device inside the grandfather clock does not record the clock ticking.
The police send radio cars to stop the motorcycle officer carrying the package back to San Francisco. However, the motorcycle clearly had a radio antenna attached to it.
The enemy agents do not know what hotel in San Francisco Barry is staying at, so they use a public phone and start randomly calling the city's hotels out of a phone book, using a nickel for each call. This would take hours as there are hundreds of hotels in the city, but they luck out and find him before he leaves. And, Barry is not even registered under a false name, even though he's a secret agent on a mission.
After the storefront is smashed in Chinatown, police bail out of an unmarked car and run to the scene. A moving shadow of the boom microphone is visible across the top of the frame.