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: At the end of the establishing continuous shot in the lobby, Bert leans against the desk and whines; "This is the kind of night that gives me the willies." The clerk rolls her eyes; she is holding a note between the two hands and you can see right before the cut that the note stays in her left as she lets go with the right. The new shoot though begins with the note in her right hand. (00:02:45)
Factual error: Charlie Chan claims that mixing hydrochloric acid with ferrocyanide of potassium is mixing two acids. Ferrocyanide of potassium is not an acid. (00:27:00)