When the briefcase containing $100 bills is opened in extreme close-up, the bills have "modern, small-size" green Federal Reserve seals that are wrong for the '30s. In that era the green seals would be much larger, and a very light green in color.
The scene transition shown when the card games on the train take place shows a Pennsylvania Railroad Q1 Class streamlined locomotive. The movie action is supposed to take place in 1936. The Q1 class locomotives weren't introduced until 1943.
In the bathroom scene Hooker can be seen saying "He didn't tell me you was a fuck-up either". This has been looped to replace it with the less profane "He didn't tell me you was a screw-up either". (The grammar error is scripted).
During "the sting", Swift is supposedly calling Lonnegan like he always has, from the Western Union office. We see earlier in the film that the office is across town. After the call is placed and Lonnegan goes to place his bet, we see Swift walk in and sit down next to him, yet Lonnegan doesn't pick up on the fact that Swift is in the betting parlor less then 5 minutes after getting a call from him from clear across town.
After Synder smashes his gun through the phone booth and hits Hooker on the side of the face, Hooker's hat falls off to the right and Hooker traps the hat between his head and the inside wall of the booth. In the next shot, Hooker is wearing his hat as if it never fell off.
During the scene in the alley where Hooker, Luther and Erie Kid are playing a con on Mottola, Hooker is "fighting" with Erie Kid while Mottola watches. Mottola's hat falls off his head to the ground, but in the next shot, his hat is back on his head.
Kid Twist tells Boudreau that Gondorff is setting up a wire on the North side. Later in the film, Agent Polk tells Lt. Snyder that, "We got a tip that Gondorff is gonna run a con on the south side here."
In the alley where Hooker, Luther and Erie Kid are playing a con on Mottola, and Hooker is "fighting" with Erie Kid while Mottola watches, Hooker grabs a wooden crate from a pile of garbage to fight off the Erie Kid. In the next shot, the box has changed significantly from a low, long dark box, to a white, shorter and steeper box.
When Hooker moves from his booth to join Doyle in an adjacent booth in the café, he leaves his hat at the far end of the bench seat, by the wall. After they end their conversation and Hooker is leaving, he picks up his hat, which is now at the near end of the seat, by the aisle.
When Johnny meets a passed-out Henry for the first time in Henry's apartment, Johnny is wearing a maroon pinstripe suit with a gray three-button collarless undershirt instead of a dress shirt. He also has a three-day stubble. The very next scene,they are both in the bathroom as Henry sobers up in the shower. This time, Johnny has on the same pants, but his coat is off an he's wearing a blue wide-collared dress shirt and is clean shaven.
The poker scene takes place aboard the 20th Century Limited, a luxury train that ran between New York and Chicago from 1902 to 1967. Arrival times in Chicago varied over the years, but they usually were between about 7 and 9 a.m. The train would not be arriving in Chicago in what appears to be the middle of the night, as happens in "The Sting."
During the draw poker hand that Gondorff wins with three 10s, there are two rules violations. After they draw cards and Lonnegan bets $500, Gondorff says "call and raise". This is not allowed; since the first word Gondorff said was "call", he would only be allowed to match the $500 bet, especially in a high stakes game (unless he was playing with extremely lenient poker players). Furthermore, he would not be allowed to raise a mere $300, or any amount less than $500; all raise amounts must at least match the amount of the prior bet.
Even though Clemens calls the poker game as "table stakes" Lonnegan goes to the bank for more money in the final hand. Clemens is not one to challenge a man such as Lonnegan over a breach of etiquette though.
In the poker game, no one buys any chips. "This is a gentleman's game, we assume you are all good for your debts." But later, the conductor has a great deal of cash, to pay people off who say: "Cash me in."
This is when the last player besides Gondorff and Lonnegan is cashing out, and he claims to have broken even, implying the other Gentleman had lost, and their chips were on the table. The remaining cash the conductor has is the lost money from those other players for the excess remaining chips on the table besides those for Gondorff and Lonnegan's personal piles.
Lonegan's last bet, $500,000.00 takes up every available inch in his briefcase- if Lonegan had won the bet (4 to 1 odds), he would have needed an additional three briefcases (which he didn't bring- nor did his bodyguards) to haul away his winnings.
Regarding the money that Hooker and Luther switch away from Motola. When Hooker goes to open the envelope in the alley, it is not sealed. It was sealed by Granger in the office before being given to Motola.
When Hooker is chased into the ally by Cole he escapes by hiding in a man-hole. However, it would take much longer to remove the heavy cast iron lid, step into it down the ladder and close the lid above him than the 10 seconds or so that Hooker is ahead of Cole.
The goof items below may give away important plot points.
Crew or equipment visible
When Cole chases Hooker into the dead-end alley and is subsequently killed by Salino, the trigger for the squib can be seen in the actor's left hand. You can also see how he uses his thumb to operate it.
When Salino is killed, the weapon in her hand is a revolver with a silencer. Since the cylinder of a revolver does not seal against the frame of the gun, a large amount of gas escapes and render the silencer mostly useless. Anyone looking to minimize noise would not use a revolver.