James Cagney had to be taught how to drive for this movie. Since he was a New Yorker without much need to drive in the 1930s, he had not learned to drive.
The film is the origin of James Cagney's famous "dirty rat" quote. What Cagney (as Matt Nolan) says is, "The dirty rat kills Danny, and you help him get away with it!" The "you dirty rat" legend, however, is traced to a few scenes later, when Matt Nolan exclaims to the killer (Buck Gerard), "Come out and take it, you dirty, yellow-bellied rat, or I'll give it to ya through the door!"
The movie-within-a-movie, 'Her Hour of Love' with Donald Cook and Evalyn Knapp, was not an actual film clip, but a new sequence filmed specifically for this movie.
To play his competitor in a ballroom dance contest, James Cagney recommended his pal, fellow tough-guy, ex-hoofer George Raft. The contest culminates with William Kenny (Raft) winning and getting slugged by Matt Nolan (Cagney) for his trouble. Within a year or so, Raft - uncredited here - would emerge as a Warner Bros. star in his own right.