Continuity mistake: After the bad guys frame Cagney for drunk driving and stage an auto accident, the smudges on his face change shape and position several times between shots. (00:27:30)
Continuity mistake: When the villain offers him a bribe, James Cagney's handkerchief keeps changing between takes, peeking out of his pocket at different lengths. His arm positions also change between shots, even though he hasn't visibly moved. (00:23:00)
Continuity mistake: When he enters Canning's office, James Cagney's coat pocket handkerchief disappears once he's inside the door. (00:39:00)