Iris' Ford sedan changes back and forth between a 1949 model (plain horizontal bar grille) and a 1950 model (with a round feature in the grille center). The dent on the passenger side of the 1949's trunk disappears and reappears.
When the hotel detective first visits Eddie and the others in the hotel room, Eddie's tie disappears and reappears.
Throughout the movie, characters clearly look off-screen and read lines from cue cards or take cues from crew.
Mooney comes to the back entrance of Universal Recorders and opens the door. From the outside view, the door opens outward. From the inside view, the door opens inward.
When Eddy asks Mooney to leave the hotel room so he can talk with his agent, Mooney walks out of the shot and the hotel door closes. Mooney's shadow is still on the wall, which means the actor is still on set.
During Eddie's recording session, his song is recorded on tape and directly to a master disc. After tape recording was introduced in the late 1940s, record companies stopped recording directly to master discs.
When Eddy and Helen are out shopping for new clothes, they stop by a bar for a drink. When they approach the door, Helen gushes about how good the food is, but her lips only move for the first line.
When the record producer calls his secretary, a woman sitting at a switchboard tells him that the switchboard is lit up with calls regarding Eddy's first TV performance. She is clearly not speaking those words.
When the gang drops by Nadine's diner after the opening heist, the shadow of the boom mic is quite visible in the top left corner as it passes over Nadine's face. Shadows of the crew are visible on the door in the back for the first 20 seconds.
When the gang returns to the hotel after Eddie tries to contact Helen at her apartment, the boom mic is visible in the hotel room.