Continuity mistake: At the beginning of the film, when Johnny is first climbing the stairway to his apartment, he climbs a flight, then there is a dissolve to imply that it's a very long stairway, and he's shown climbing another flight. You can see the ground floor only one flight below after the dissolve.
Continuity mistake: When young Johnny goes over to Dundee's car to talk to him, he leaves his bag of newspapers on the sidewalk. When he walks away from Dundee's car after talking to him, his bag of newspapers is over his shoulder.
Continuity mistake: After Moronie's robot has finished emptying his machine gun at the Dundee gang, the machine gun is pointing straight out. Then, when Johnny gets the note from Moronie, the robot's machine gun is pointing straight down.
Continuity mistake: When Johnny gets knocked out when trying to leave the crime commissioners office, his arms are down by his side while on the ground. In the next shot of him lying on the ground, his arms are straight out from his side.
Continuity mistake: When Johnny comes into the theater and sees the gun, the screen has a horizontal tear in it. But shots from behind the screen just have a vertical cut. And it's not like the gun was blocking the view since Danny pulled the gun out of the slit and there's no horizontal tear.