Over the course of the film, Dunne's shaved unibrow changes at multiple times. Sometimes there's hair in the center of the brows, sometimes fully there, sometimes completely gone, and sometimes hair parallel off the center.
When Paul is running from the mob, he seeks shelter in the coffee shop and orders hamburger and coffee. The clock on the doorway shows 4:10. But when he is again running from the mob and goes there to meet Tom, the same clock shows 12:14 when the waiter brings him hamburger and coffee. Moments later, it says 5:00.
When confronted by Tom's neighbors, Paul says he's a friend of Tom's, but during their initial meeting in the bar, Paul and Tom do not exchange names.
When Paul is talking to Julie outside the closed bar and Neil and Pepe drive by, it can be seen that Neil is driving and Pepe is in the passenger's seat. But then it's suddenly Pepe driving and Neil telling him to speed up.
Paul looks at his watch a couple of times in the early part of the film and it has a black face. When he is in Julie's apartment he is wearing a watch with a white face.
June addresses Paul by his name twice, although he never tells her his name.
On "Mohawk Night" at the Berlin nightclub, only one person in the crowd is wearing a Mohawk haircut.
The music playing during the end credits is Wolfgang Amadeus Mozart's Symphony 45 in D, K.95:1. Allegro, which is not listed in the credits.
The sound of a mousetrap snapping shut in Julie's apartment is clearly that of an empty one with the sharp sound of the metal trap bar loudly making contact with bare wood. The sound of one snapping down on an actual mouse would make more of a dull thump rather than a loud clack.
After Paul and Horst's exchange about his rudeness to Marcy, Kiki says to Paul "Well it's not too late to finish what you've started" though when she says the word "well" her mouth doesn't move.
When Neil and Pepe flee from Paul in the van (the first time), the engine can be heard revving as they speed away although the brake lights are on.
Boom mic visible in reflection of mirror.
When Neil and Pepe emerge from June's underground apartment, a street sign directly behind them says Spring St. According to Kiki, Club Berlin is on the corner of West Broadway and Grand, several blocks south of Spring.