Continuity: Towards the end of the opening scene, the cigar on Leo O'Bannion's desk mysteriously changes position, although it eventually returns to its original location.
Continuity: The position of the police chief's arms while talking to Tom during the attack on Leo's club.
Continuity: Tom's whiskey glass on Leo's desk disappears after he confesses to Leo.
Anachronisms: The US flag in the mayor's office in the 1920s appears to be a 50-star flag.
Continuity: When Tom throws the glass at the mirror in the woman's washroom, the cracks in the glass change between shots.
Continuity: When Verna and Tom are talking in the women's restroom, Verna slugs him. As he staggers away, the glass is in his left hand, but he throws it at the mirror with his right.
Continuity: After the Sons of Erin club blows up, a burning body flies out onto the street. In the subsequent shots, it is gone.
Continuity: When Tom is picked up by TicTac and The Dane before they go looking for the body in the woods the street changes between shots - a black car appears beneath the High & Sons sign in one shot then disappears when TicTac swerves his car onto the pavement
Continuity: The robe that Verna wears when Tom visits her the morning after he loses his hat keeps changing positions between shots, alternately revealing and concealing her bra.
Revealing mistakes: In the scene where the little boy finds Rug Daniels in the alley, as he takes off his toupee, his mouth and right eye move slightly.
Continuity: When Tom is taking Bernie out into the woods, in one shot Bernie's shirt is clean, in the next it is very dirty.
Revealing mistakes: When Tom and the other mobsters go into the woods and find the dead man, for a brief moment, his face can be seen to flinch.
Anachronisms: Verna dials 911 when Tom Regan comes to her apartment, on the night of the hit on Leo's house. In those days, you had to dial 0 and ask for the police if you wanted them quickly, but then again, there were operators by the hundreds available at the spin of a rotary dial.
Factual errors: In the scene where Leo uses the Thompson sub-machine gun he should have had to reload at least 6 times. Assuming the gun is a 1928 model the rate of fire is 700 rounds per minute and has a 100 round can of ammunition. The gangster walks into the bedroom and fires for 5 seconds for a total of 58 shots fired, Leo takes his gun and fires at the window for 20 seconds for 233 shots fired, then Leo fires at the car for about 20 more seconds for another 233 shots fired. That is a total of 524 shots fired from one Thompson with no reload.
Audio/visual unsynchronized: When the Dane goes to Verna's apartment, Verna pulls a gun out of her purse on the bed and points it at the Dane. He then slaps her hand with the gun, but the sound of the slap is clearly before the visual.
Audio/visual unsynchronized: When Johnny Caspar is being driven up to Tom Reagan's apartment building he is talking about how to get a perfect shave but his mouth is not moving.