When Carmine's goon pretends to talk to Abe, Abe takes his earpiece receiver out of his chest pocket and holds it before him. When the camera cuts to the wide shot, it's back in his chest pocket, and he takes it out again.
When Brick is signing the register, his left hand goes from being on the register in the closeup to under his right hand in the wide shot. His collar and Abe's pose change instantaneously as well.
When the patron with bicycle is signing the register, Abe turns to unlock his locker twice.
When Carmine first calls Claude from backstage, Claude's wig is pulled forward. When he says, "Fashionable", the wig is far back on his head in the closeup. When it returns to the long shot, the wig is forward again.
The sign advertising amateur night is misspelled "amatuer". However, signs often have misspellings, so this should not be considered a Goof.
The movie is set in New York (and briefly, Cleveland). Gaetano and Vivian Proclo are clearly Italian-American, yet their daughters speak with distinctly British accents. The movie was filmed in England.
Googie tells Gaetano before the show that her second number is "Shine On, Harvest Moon". On stage, her second number is "Begin the Beguine".
After Chris tells Carmine that Proclo is in Claude's room, he runs away without looking where he is going and accidentally slams the side of his head into the narrow door jamb.