- Cast the Runner-Up: Edward Woods was originally hired for the lead role of Tom Powers and James Cagney was hired to play Matt Doyle, his friend. However, once director William A. Wellman got to know both of them and saw Cagney in rehearsals, he realized that Cagney would be far more effective in the star role than Woods, so he switched them.
- Enforced Method Acting: The machine gun attack on Tom and Matt actually used real machine gun bullets. An expert with the gun stood on a raised platform 15 to 20 feet away from the target, and when James Cagney's face disappeared behind the corner of the wall, he opened fire and created that tight circle of machine gun bullets.
- I Am Not Spock: Because of the famous grapefruit scene, for years afterward when dining in restaurants, fellow patrons would send grapefruit to James Cagney, which—almost invariably—Cagney would happily eat.
- Real Song Theme Tune: "I'm Forever Blowing Bubbles"
- Star-Making Role: For James Cagney.
- Uncredited Role: Mae Clarke is uncredited as Kitty.
- What Could Have Been:
- In the original script, James Cagney was to stuff an omelette into Mae Clarke's mouth instead of a grapefruit to the face.
- Louise Brooks was offered the role of Gwen Allen, but Brooks turned down the offer in order to visit her lover George Preston Marshall in New York City, and the role instead went to Jean Harlow, who then began her own rise to stardom, while in the opinion of biographer Barry Paris, "turning down Public Enemy marked the real end of Louise Brooks's film career."note Although Brooks later claimed she declined the role because she "hated Hollywood," film historian James Card, who came to know Brooks later in her life, stated that Brooks "just wasn't interested ... She was more interested in Marshall."
Trivia / The Public Enemy (1931)