Factual error: In the scene where all the heads of families meet shortly after Sonny's death, there is an exterior shot of a large grey-brick building with an American flag hanging from it. If you look carefully, the flag is a current flag with 50 stars, with alternating rows of indented stars. But, the scene is takes place circa late 1940's when there were only 48 states and all the rows of stars were even. (By the way, the flag inside the meeting room is the correct one.)
Continuity mistake: When Diane Keaton and Al Pacino have dinner, he gets up, puts on his coat and sits down again. Now watch Diane Keaton's glass: When the camera's on Al Pacino she's holding the stem, but when the camera's on her she's holding the body of the glass. Another mistake is that at the end of the scene the amount of wine in her glass suddenly doubles.
Other mistake: After Sonny is shot on the causeway, there are a very large number of bullet exit holes visible on the sides of the tollbooths, which could only have been made if the gunmen shot through the walls (not the windows) of the buildings from the inside. This is common in movies. In real life, bullet entry holes in wood appear as small black dots, not the more dramatic-looking splintered gashes made on the other side of the wood as the bullet exits.
Continuity mistake: When Tessio delivers the bulletproof vest and the fish, Sonny's hands are in one position (one below, one on top of the parcel), a fraction of a second later they are in a very different position (both on top, unwrapping). The parcel is half open while Tessio is carrying it but fully closed when he puts it on Sonny's lap.
Continuity mistake: When Don Vito Corleone gets shot, the camera angle from the side of the car shows Fredo bent over trying to pick up the gun he dropped, but when we see him from the camera angle from above, he's just walking to the front of the car. When the angle cuts back to the front of the car, Fredo is once again bent over trying to pick up the gun.
Continuity mistake: Before Paulie is shot, Clemenza gets out of the car to relieve himself and walks only a few steps away from the car. As Clemenza hears the gunshot, he looks back at the car to see Paulie slumped over the steering wheel, and the car is a much greater distance away, than just the few feet he had walked away from it. As Clemenza walks back to the car, it again takes him only a mere few steps.
Continuity mistake: When they're all deciding whether to wait until the Don is better before making a deal with Sollozzo, the cigar box is closed. The camera cuts away for a second, then back and Sonny closes the miraculously open box. He can't have opened it while the camera was elsewhere, because opening it would have taken the lid right past the camera.
Continuity mistake: In the first scene, the undertaker Bonasera asks the Godfather for help. When the Godfather gets up from his desk, the rose in his lapel is either fresh and straight or slightly wilted and bent in alternating shots. Also, later in the wedding scene, this rose keeps recovering from intermittent spells of withering.
Revealing mistake: When Michael is riding in the car with Sollozzo before the assassination, notice the headlights in the rear window during the close-up. You can notice that many of them move directly on top and underneath each other, impossible for real car's headlights to do such a thing.
Continuity mistake: Outside the hospital McCluskey punches Michael. A few days after the episode outside the hospital, Michael shoots McCluskey and Sollozzo at the restaurant, but there is no mark on his face where he was hit. Then in Sicily when Michael meets Apollonia for the first time, there is still no mark on his face, but suddenly at Apollonia and Michael's wedding, he has a large mark on his face.
Factual error: The Cadillac Miller and Cadillac Meteor flower cars at Vito Corleone's funeral are an anachronistic impossibility, given that he died some time in the summer of 1955. With two exceptions (one from 1951 and one from 1955), the Cadillacs serving as flower cars are 1956 models. Although a 1956 Cadillac Fleetwood 75 limousine also makes an appearance, it's plausible that the funeral could be taking place at a time when the first 1956 Fleetwood 75's were released. Miller and Meteor, however, did not begin converting 1956 Cadillacs into flower cars until 1956 proper.
Continuity mistake: When Vito Corleone gets shot, he rolls on his back and his coat opens up to show his shirt. Then we see Fredo sitting down on the nearby steps and crying. In the next wide shot, Vito is lying on the side, totally covered by his coat, and Fredo is sitting farther away than where we saw him before.
Factual error: On the way to the meeting when Michael is going to kill Solozzo, the car made a U-turn on the George Washington Bridge (GWB), which connects Manhattan to New Jersey. However, the scene is shot on the Queensborough (59th Street) Bridge, which connects Manhattan to Queens. They look nothing alike, the GWB is a suspension bridge, the Queensborough Bridge is a cantilever bridge.
Continuity mistake: When Michael Corleone goes to Las Vegas to meet with Moe Greene, watch carefully when Moe sits at the table while continuing his argument with Michael. There's a glass of water that changes places from shot to shot. At one moment, the glass is behind Moe's arm, then in the next shot it's in front. Moe moves the glass at one point, but nevertheless, the glass continues to move from shot to shot.
Factual error: When Luca Brasi goes to meet the Tattaglia family and Sollozzo to pretend he would like to defect, and they garrote him, Brasi is making all kinds of loud noises while being strangled until he dies. During choking or strangulation, one is unable to make much (if any) sound because air cannot pass through the vocal chords on its way out of the body just as it cannot enter the body and get to the lungs.
Continuity mistake: In the meeting of the heads of all families, when Tattaglia asks the Godfather for assurance that there will be no vengeance, we see him leaning back in his chair, waiting for an answer. In the next shot the camera is on the Godfather, and we see Tattaglia leaning back again.
Continuity mistake: At the restaurant, Michael, Sollozzo, and Captain McCluskey have just sat down at the table and the waiter comes over to take their order and pour wine. Sollozzo recommends that McCluskey try the veal, but McCluskey is already eating his dinner. By the way he is using his knife and fork, it is obvious that he is eating an entree, not a salad or an appetizer, even though they just arrived.
Factual error: In the establishing shot of the movie producer's mansion, a car in the driveway is suppose to be a 1937 Cord, but actually it is a replica produced between 1968 and 1972. Real Cord cars had bug eye headlights that cranked out of the fenders. The replicas had fixed glass covered headlights in the fenders.
Factual error: Michael had his meeting withe Solozzo around Christmas of 1945. On the way to the meeting, the car made a U-turn on the George Washington Bridge (GWB) to throw off anybody who might be following. At the time, the GWB had four traffic lanes, two in either direction. The median between the two set of lanes was about 20 feet of steel mesh, making such a maneuver impossible. The median was filled in to add two additional traffic lanes in 1946. At that time, the u-turn would have been possible.