When John Hoyt as Dreyer reaches into his desk for a gun, the contents of the desk on the insert close-up do not match the contents on the master shot.
In the scene where Susan is having a drink in her apartment, there are shadows of plant leaves on a door in the background. However when Mr Brown comes in via another door, these shadows have vanished in the ensuing shots.
In the final scene at the airport, the position of the spotlight attached to the car that Susan keeps aiming at Brown changes from the top of the windshield to the bottom and back again.
Although by the opening shots this film takes place in New York City, police cars shown have the seal of the city of Los Angeles on their doors.
Joe McClure is not completely deaf; his hearing aid would be useless if he was completely deaf. Just before having Joe McClure killed, Mr. Brown removes Joe McClure's hearing aid, so he won't hear the gun shots. Gun shots are extremely loud, Joe McClure would still hear the gun shots without his hearing aid, the sound would only be reduced without his hearing aid. Only a completely deaf person would not hear gun shots.
The rotating beacon light at the airport is pointing down instead of straight out parallel with the ground.
Throughout the movie Lee Van Cleef's character is addressed as Fante and Earl Holliman's character is addressed as Mingo. In their last scene at the end of the movie Lee Van Cleef becomes Mingo and Earl Holliman becomes Fante.