When Slaughterhouse is dividing up the money, the cash wad mysteriously switches from being held in both hands to just his right hand.
When 'Slaughterhouse' Scorpio (Wallace Beery) shoots Johnny Franks (Ralph Bellamy), the view is of Franks from behind and only the gun smoke and sound of an automatic weapon firing from just off-screen. When Scorpio is shown immediately afterward, he is holding a revolver and not an automatic weapon, so obviously the two scenes were shot separately and patched together.
When Jean Harlow runs into the subway, she rushes through the turnstile without paying and onto a car. In real life, if she had not put in a token, the turnstile bar would have prevented her going on to the platform.
The DA tells the Secret Six that six policemen were killed and two fatally wounded.
The last name of "The Gouger" is spelled "Mizoski," but on the billboard on top of the building (a process screen long shot leading into the political rally at the slaughterhouse) it is spelled "Mazoski."
Although supposedly set in Chicago, after the shoot-out in the bar, as the gangs drive off on the rear-projection in the background can be seen the large vertical sign for the Metropolitan Theater in Los Angeles (at the corner of 6th and Hill Streets). That footage was also shot in 1929 or before as during that year Paramount bought the theater and renamed it "The Paramount). The distinctive 5-globe Llewellyn Iron Works streetlights are also a giveaway those shots were done in L.A.