This is the one episode where Jack Benny actually plays the violin well--in this case to prove to Professor LeBlanc that he has learned how to play the violin correctly.
"Professor LeBlanc" is, of course, Mel Blanc, that master of voices who provided the cartoon voices for, among others, Bugs Bunny, Porky Pig, Daffy Duck, Sylvester the cat, Foghorn Leghorn, Pepé Le Pew, Wile E. Coyote, and Yosemite Sam.