Grapefruit!

Has everyone missed the hilarious connection between Cagney and grapefruit in this film? The whole Grapefruit Acres scheme, the grapefruit diet, and Cagney saying to the DA he's never even seen a grapefruit? All this after his famous grapefruit-to-the-face scene with Mae Clarke in "The Public Enemy" (1931) just two years previously. Is this whole sub-plot a huge inside joke? I thought it was hysterical! How did everyone keep a straight face?!