James M. Cain, whose story "Two Can Sing" was the basis for this film, had himself trained as an operatic baritone. Opera figures prominently in several of his other stories, including "Serenade" and "Mildred Pierce" (though the opera parts of the plot of "Mildred Pierce" were dropped in the film version).
When Nunnally Johnson remade the picture as Everybody Does It (1949) he used the exact same script without doing any rewriting.
Leonard's mother-in-law complains that for three years she talked to her husband about Wagner until she realized he thought she meant the ballplayer. This would have been Honus Wagner, the great shortstop for the Pittsburgh Pirates in the early years of the twentieth century.