To silence Sylvester, who is "singing" late at night, Elmer heaves a book at him, which Sylvester promptly throws back. The book Elmer tosses is titled "The Thin Man". The book Sylvester throws back is titled "Return of the Thin Man".
Sylvester's version of "Angel in Disguise" is done in the style of Spike Jones, right down to Sylvester starting the song in an operatic voice (without the lisp), the wacky sound effects, the brass, banjos and tubas.
A 1941 black and white WB cartoon, Notes to You (1941), featuring Porky and an alley cat, had much the same plot. However, instead of "The Thin Man" book gag, the tomes used here were from "Dr. Fu Manchu."