Young Henry is right-handed, older Henry is left-handed.
When Karen holds a gun in Henry's face, one gun is used in close-ups, and a different gun is used for long shots.
When Karen visits Henry in jail the daughter sitting on her lap plays with blocks. These blocks change between shots.
When Sonny Bunz has his sit-down with Paulie about Tommy, an over-the-shoulder shot from behind Sonny shows Paulie talking with a cigar in his mouth. In the next shot, an over-the-shoulder shot of Sonny, Paulie's cigar is gone. In the following shot, another over-the-shoulder from behind Sonny, Paulie has the cigar in his mouth again.
When Henry and Karen go on their first date alone, their clothes are different when they arrive at the club.
Paulie was sent to prison for fraud, not contempt as Henry states.
In 1963, Henry and Tommy are grown up, and leaning against the trunk of a 1965 Chevy, while waiting to steal a truck.
According to ex- mobster Michael Franzese, Hill was not as close to Cicero as the film portrays. Also, Hill developed alcoholism in addition to drug use during his life.
Henry Hill is portrayed as a powerful and important mob associate, involved heavily in many of their illegal activities and being friends with mafia dons. In reality, Hill was a hanger on and minor mob associate.
When Henry says "Air France made me. . .", the aircraft shown is a Convair 240, which Air France has never flown.
During the "You're a funny guy" scene, set in 1963, a bottle of Crown Royal whiskey is on the table. Crown Royal wasn't sold in the US until 1965. Tommy smuggled it into the States.
During the prison dinner scene, Paulie says, "Freddie, Vinnie, come eat." According to the montage 17 minutes into the film, each gangster has at least one nickname. Freddie could be a nickname for Johnnie Dio.
When Henry has the phone cord around Morrie's neck, the phone receiver is clearly in his hand. The phone rings, which can't happen when the receiver is off the hook.
During the Morrie's Wigs commercial, Morrie jumps into a swimming pool to prove his wig will stay on underwater. When he emerges from the water, his head is bone dry. It's most likely intentional, to hide the fact that the wigs may not behave underwater as advertised.
When Henry smuggles cheeses, wines, and scotch into prison, he says "Vinnie, I got your peppers and onions" when talking to Johnnie Dio. Henry mentioned earlier that every gangster has at least 1 nickname; Vinnie could be Johnnie Dio's nickname.
After Morrie is killed in the car, he blinks when Frankie Carbone opens the driver side door.
In the steadicam scene at the Copa, Henry and Karen's route doubles back on itself in the kitchen. As they turn left to enter the kitchen, a fire hose is behind a waiter in front of them. Thirty seconds later, they emerge from the same door with the fire hose on their left. They could've passed the kitchen door and turned right, into the nightclub.
When the mailman's head is pushed into the pizza oven, his hand is clearly resting on the inside of the oven door before the image is frozen. A cooked pizza is inside the oven as it's opened, so it should be too hot for him to keep his hand there for more than a few seconds.
When Henry and Karen are at the Seaside resort, Henry tries to pay the bill with cash but Karen says he must sign for it. All of the $50 bills in Henry's hand have the same serial number.
When Henry brings the guns for the silencers that have already been purchased, the silencers are threaded and the barrels are too big. In reality, gun barrels are threaded and the silencers fit over them.
When Henry and others are outside Idlewild Airport in 1963, and overhead a Boeing 747 flies overhead. The first 747 test flights were in 1969, and they entered service in 1970.
In the scene that opens with "Idlewild Airport, 1963", Henry leans on a 1965 Chevy Impala.
When young Henry Hill is arrested for selling black-market cigarettes, the cartons have UPC barcodes. A barcode is also visible on a bottle of dish soap on the window sill as Johnny and the boys are making spaghetti in the late 1950s. Barcodes were introduced in 1966, became an industry standard in 1970, and were first scanned in 1974.
In an early 1970s scene, Visa and Mastercard logos are on the front door of a restaurant. At the time, Mastercard was Master Charge, and Visa was BankAmericard.
Near the end, when Henry is driving around watching for the helicopter, a package of Winston cigarettes is on the dashboard of his car. The scene is set in 1980, but the package design was introduced in 1987.
When Karen screams, "He pushed me out of the car," her mouth is not moving.
When Jimmy, Tommy, Carbone, and Morrie get in the car just before Tommy kills Morrie, 4 car doors shut when Morrie is still standing with the passenger door open.
When Janice hands her dog to Tommy, Tommy's voice says "I'm gonna eat this fucking dog", but his mouth says something different.
When Tommy shoots Stacks Edwards, he does so with a .45 auto outfitted with a silencer. The sound effect is the typical airy 'pop' of silenced guns in the movies. However, when the scene is replayed in slow motion as Henry narrates that the getaway van was found, the slow motion sound effect of the gunshots are of unsilenced 'bangs'.
When Billy Batts says, "What?" to Tommy in the bar, Billy's lips don't move.
When Jimmy calls about Tommy being made, the front of a camera is reflected in the side of the phone booth.
When Jimmy Burke's character is introduced, the camera pans around the room. A stage light is visible in the upper right corner of the shot, traveling with the camera as it pans.
When Henry and Karen hide the gun at her mother's house, a camera is visible in the background.
When young Henry enters the phone booth as he and Tuddy Cicero are "running around" making Paul's phone calls, a wireless mike pack is in his back pocket.
About 45 minutes in, a camera operator is visible on the right side of the screen.
The Airline Diner is outside Laguardia Airport, not Idlewild (now J.F.K.).
The mob men grab Henry's mailman leaving work from a post office named "Pitkin Ave Station, Queens, N.Y.". Henry lives in East New York, Brooklyn, which would be in a different zip code.
Cicero's associates may have prevented any letters from Henry's school from reaching his home, but the school could still call his parents on the telephone.
When Henry is released from prison, the mic is reflected in the car window when Karen turns to her right to hug Henry.
Shadow in Henry's house when he is talking with Marie about the Lufthansa heist.
the frozen body in the meat truck has tiny movements in the wrinkles of his eyes, about the same time the narrator speaks of the solidly frozen state of the body.
Early in the film, Henry's voiceover states that Jimmy Conway (Robert De Niro) is 28 years old. However, De Niro was in his mid 40s when portraying this character, which is obvious.
In an early scene, the narrator says, "It was before Apalachin," referring to the upstate New York town where a late-1950s Mafia summit was raided by police, making national headlines. He pronounces it "ap-a-LAY-chin," instead of "ap-a-LAY-kin."
When Henry and Karen are on the floor of their bedroom, and Henry points the gun to her face, he accidentally steps on her hand when he gets up.