(at around 33 mins) As Evans and Pardo drink coffee, Evans' coffee cup changes several times from a dark cup to a light cup.
In the last scene after Cody and the gang try to escape the refinery (after the Police presence has been made known), the day-to-night continuity during the escape/shoot-out scene changes far too fast. After a Police character says "Get some search lights," the film goes straight from noticeable day-for-night photography to actual night photography.
When Cody, Velma and Ma duck into the drive-in theatre to evade the police, the film showing is TASK FORCE which Ma Jarrett also states was the movie playing when questioned by the police the next day. However, a close look at the marquee on the drive-in theatre reveals that the film playing is SOUTH OF ST. LOUIS.
The fabric marker on Ma Jarrett's car changes positions.
In the machine shop, after Parker decides to drop a motor from an overhead crane onto Cody he moves the scrap metal barrel to the middle of the aisle. There is scrap piled toward the top of the barrel but in the next shot of the barrel it appears empty with no metal showing.
No modifications were shown being made to the tanker truck. And there were no modifications that could be seen inside the tank. But yet, when they use it to hide in to get into the refinery it's just a wide open tank inside. Tanker trucks are never just open tubes. They have perforated dividers called baffles that reduce the effects of the fluid sloshing as the truck moves.
When Cody is ventilating the car trunk for Parker, he is using a Colt 1911A1 pistol. When he runs out of bullets, the gun clicks when he pulls the trigger -- on a 1911A1 when the magazine is empty, the slide locks back and pulling the trigger does nothing - that doesn't happen with Cody's gun.
In the final scene Cody shoots the natural gas tank which ignites a fire and causes the entire tank to explode. Soft lead bullets would not create the spark necessary to ignite the gas contrary to what Hollywood writers constantly do. In addition, the pressurized gas would just burn without causing the massive explosion because fuel needs air to burn and none could get into the tank through the bullet holes because the pressurized gas would be streaming out.
Near the end, Cody Jarrett (James Cagney) fires his shotgun at a couple of cops. One cop is hit and goes down but the other cop (standing close to the downed cop) remains standing.
The gas station attendant removes the radiator cap with his bare hand.
After the train job at the first hide-out, some of the gang is gathered around the 1947 Cadillac 75 limo listening to the radio news about their caper. A shot of the interior shows a chrome "Cadillac" script on a plate above the radio speaker grille. This plate must be removed when a radio is installed as this is where the dial, controls, and push buttons are located. Since the plate is still present, it means in reality there is no radio in the car.
Big Ed's corpse breathes.
Near the start of the film, Big Ed and his thug pal hold the conductors hostage and direct them to stop the train when they tell them to. When the conductors are put out of action, Big Ed (Steve Cochran), pulls the emergency cord himself to stop the train, showing there was never any need to get the conductors involved at all.
In the shot looking toward the ceiling of the prison machine shop, showing the piece of equipment Parker plans to drop on Jarrett supposedly dangling directly over Jarrett's head, it is clear that the object is in fact well to the right of Jarrett (from his perspective), undoubtedly a precaution by the filmmakers so that it would not accidentally fall and hit actor James Cagney (Jarrett).
At the end when Fallon is shooting at Jarrett, Evans shows the side of the bullhorn labeled "Warner Bros. Elect. Dept. P.A."
Cody shoots Parker through the lid of the trunk of the car with a Colt 1911. When he runs out of ammo, it simply clicks. But the slide of a 1911 always locks to the rear after the last round is fired. His doesn't.
When the gang is leaving the hideout on the way to rob the refinery, the shadow of a camera can be seen on the side of the gas tanker as it pulls onto the road.
In the opening railroad heist, there is a shot of a man jumping down from a tunnel portal onto the train. When he lands the mats used to break his fall can be clearly seen.
Roughly five minutes into the movie during the train robbery, one of the robbers gets accidentally blasted in the face with steam from the locomotive. As three men pick up his body the area where the head belongs is suddenly a protruding section of metal that holds the mannequin's head in place. The body is clearly a mannequin without a head.
In two different scenes, police cars pass in front of the same supermarket, though one scene is supposed to be in Los Angeles and the other in Illinois.
The police, planning to travel from Los Angeles to a state prison in Illinois, would probably have planned to fly to Chicago and not Springfield. The envelope sent to Vic / Hank only says "state penitentiary, Ill.," but they probably would have been in Joliet or Pontiac, both in NE IL.
The character of "The Reader" is called "Herbert" by Cody in a scene in their cell and by his lawyer during a conversation in the visitors room. Yet when Evans is listening to the police radio broadcast giving the names of the convicts who escaped with
Jarrett in the prison break, The Reader's name is given as "Michael Curtin."
When Cody is in the shoot-out with the Police towards the end of the movie he is up high on a platform. Just before he shoots his revolver he closes his eyes and flinches before he pulls the trigger on his gun.
When Ma Jarrett is shopping for strawberries and is seen, the detective leaves the store carrying a bag of produce. It is difficult to determine whether he actually takes the bag into the phone booth with him, but there is nowhere outside the booth to place the bag, but there was a shelf inside old phone booths. Either way, when he exits the booth he no longer has the bag, and as soon as he ties the rag to the car bumper, he walks down the sidewalk, away from the booth where the bag may have been left.
At the motel Cody says to his wife and his Ma, "We'll leave the sedan, that's the car they've been lookin' for.... I'll get the coupe," but the gang doesn't have any coupes. The Mercury they leave in is a sedan too.