When the Godfather is talking to Johnny Fontaine in his office, Sonny Corleone is also present. Then, the scene cuts to the entrance of the wedding cake outside. Sonny can be seen with the white flower in his lapel standing by the cake. Then, the scene goes back to the office where Sonny is still present with the Godfather.
The waiter fills Tom Hagen's glass twice within seconds during his dinner with Woltz.
Enzo (the baker) visits Don Corleone in the hospital after he is critically wounded. Enzo is holding a large bouquet of pink carnations and baby's breath. Later, when he is standing outside the hospital with Michael, the bouquet has been changed to a much smaller one with orange carnations.
When Don Corleone is talking to the pastry shop owner during the wedding scene, the man is holding a small shot glass. As he is getting up to grab Don Corleone's hands, the glass is still in his hand but in the next shot it is gone.
In the wedding scene, immediately after Kay Adams meets Tom Hagen, the cigarette in her hand disappears and then re-appears.
The use of the title 'Don' is incorrect as the proper use of this term of respect is always attached to the individual's first name, not surname. Marlon Brando's character should have been addressed as Don Vito, not Don Corleone. Same rule would apply to the other 'Dons'... Barzini, Fanucci, etc.
When seen in uniform at the wedding, Michael's shirt collars are missing his captain's bars. Marine Corps officers wear their rank insignia on their shirt collar points as well as on the epaulets of their coats.
The typefaces shown in the headlines of the various New York City newspapers depicted are almost all incorrect for the newspapers shown.
When Don Corleone stops to buy fruit, there is a pile of oranges. In 1945 you could not get oranges in NYC in December.
If Capt. McCluskey had broken Michael Corleone's jaw, then Michael should not have been able to talk so soon afterward, when he's discussing the hit on Capt. Mark McCluskey and Virgil 'The Turk' Sollozzo in the restaurant. His jaw would have been wired.
The punch to Michael's face broke his cheek bone which gave him a permanent black eye (and caused his sinuses to continually run - hence the use of a handkerchief all the time) until he got back to America and had surgery to fix it (Freddie says, "that doctor did a good job.")
The car Michael and Apollonia drive is a right-hand drive, whereas Italy drives on the right and you would expect vehicles to be left-hand drive. However Italian car manufacturers Alfa-Romeo and Lancia continued to produce cars with right hand drive for sale in Italy until the 1950s.
The exterior set-up shot for the summit meeting of all families is of the Federal Reserve Bank of New York. While this seems like an unlikely place for a "family" meeting, it's an indication of how high their influence reaches.
When Michael is moving Vito to a different room in the hospital with the help of the nurse, we can see that Marlon Brando instinctively moves his hand when it hits the door post. However he is conscious, hence his crying while Michael is holding his hand, just heavily sedated due to the pain inflicted by his gunshot wounds.
Peter Clemenza's house has an A/C hanging out the window. However, window air-conditioners were first marketed in the mid-1930's - and, even though they were expensive, Clemenza would have been able to afford one.
Outside the hospital, as Capt. Mark McCluskey prepares to punch Michael Corleone, as the shot changes showing McCluskey (Sterling Hayden) punching Michael, it is clearly not Sterling Hayden throwing the punch as evidenced by the longer, brown hair of the man doing the punching (vs. Hayden's short, grey hair).
Watch closely during the fight between Sonny and Carlo and you can see Carlo slightly jumping as Sonny throws him over the little fence.
During the sequences filmed in Sicily, Michael's broken-jaw make-up does not match the make-up used during the sequences filmed in New York. This is because Paramount Pictures would not pay the costs of sending makeup artist Dick Smith to Italy with the rest of the crew.
When Cuneo is killed in the revolving door, the bullet holes appear too late after each shot. The holes also appear nowhere near where the gun was aiming when fired.
When Sonny is beating up Carlo, the actor is momentarily changed to a stuntman who doesn't look much like Gianni Russo.
When Sonny beats up Carlo, James Caan can be clearly seen in profile faking a punch so badly that he misses Gianni Russo by a foot and a half, with his fist passing within eight inches of his own chest.
When Michael is at his father's funeral he says he will meet with the heads of the 5 families. But since he is the head of one of the families he should have said he would meet with the other 4 heads of the families. Moe Greene was not a family head.
Kay's hair style when she and Mike are having dinner just before he goes to the hospital to see his father is more suitable for later decades. However, it does resemble some hairstyles of Doris Day of the early 1950s.
Michael Corleone supposedly won the Navy Cross during World War II, but the ribbon for the Navy Cross does not appear on his Marine uniform at the wedding party scene in The Godfather.
During the hospital scene, as Michael and the nurse are wheeling Vito's bed into the storage room, they almost pinch Vito's hand in the door frame. He jerks his hand out of the way.
When Michael is arriving in Las Vegas, supposedly set in the very early 1950s, when he, Fredo, Tom and others are getting out of the car in the hotel driveway, two long-haired, bearded "hippie types" from the early '70s can be seen through the window in the lobby. (In the DVD commentary, Francis Ford Coppola admits that he is embarrassed by this oversight, but that the shot was done on the cheap by the second unit.)
50 star U.S. flag in 1947 (on the building where the "peace conference" is held).
When Michael finds his father without protection in the hospital, he picks up the phone by the bed to alert the family. The receiver has a curly cord which wasn't available until the mid- to late-1950s.
When Capt. Mark McCluskey confronts Michael Corleone outside the hospital, the sound of a conversational, female voice is heard emanating from the police vehicles' radios. At the time, however, the New York Police Department's primary radio system was based solely on one-way broadcasts from headquarters, with male police officers behind the microphone.
When Michael moves his father's bed from the hospital room into the hallway, there is a sign on the wall over Michael's shoulder which lists Robert O. Lowery as the Fire Commissioner. He was Commissioner in the 1970s, not the 1940s (it should have been Patrick Walsh).
During Sonny and Carlo's fight, one of Sonny's "movie" punches is shot from the wrong angle and clearly misses, but still produces the sound of an impact.
When Moe Greene says his line "I talked to Barzini", it's obviously dubbed in.
When Virgil 'The Turk' Sollozzo releases the abducted Tom Hagen, he says to him "... and bad luck for you if you don't make that deal!". His lip-movements, however, show that he only says "... and bad luck for you!"
When Don Corleone is heard, off camera, introducing the heads of the other families and where they're from, at the meeting, his voice is noticeably different than it was in scenes before or after.
In Vito's brush with death, one hitman's pistol emits a muzzle flash, visible just after a cut to the overhead shot of them running away, but there is no accompanying sound effect for this last gunshot.
When Carlo kicks the bathroom door trying to beat Connie, the camera is visible for a few frames through the mirror on the door.
After shooting Virgil 'The Turk' Sollozzo and Capt. Mark McCluskey, Michael Corleone walks into the camera.
When Fredo enters the car to drive just before Don Corleone's assassination attempt, you can clearly see a male crew member's face in the driver's side mirror as he opens/closes the door.
When Virgil 'The Turk' Sollozzo takes Michael Corleone to the restaurant for their conference, his car drives onto a bridge, where Michael sees a sign reading "To New Jersey", and he asks, "We're going to Jersey?", just before the car U-turns in mid-span. In fact, the only bridge between Manhattan (where they picked Michael up) and New Jersey is the George Washington Bridge, and the bridge on which the car is shown is definitely not the GWB. (It may be the Williamsburg or 59th Street bridge.)
Lou would have shot Michael when he left the restaurant on his own.
To allow Michael to assassinate the Turk and McCloskey, the Corleones have to go through a risky scheme involving hiding a gun in a public bathroom and hoping Michael can find it. Their plan also requires Michael having to flee the country as a murder suspect and runs the risk that he could be convicted and sentenced to prison for life. However, once they know the location of the meeting they could have other hit men come in and carry out the assassination, thus avoiding any risk of Michael not finding the gun and reducing the chance that he gets blamed for the killings.
Virgil "The Turk" Sollozzo would have had a couple of his men at another table in the restaurant.
The attempt on Vito Corleone's life does not make strategic sense. If his contacts in politics and the judiciary are critical to the protection of the narcotics industry, then they will be lost if he dies. As Hagen says 'If the old man dies we lose half our political strength'.
The Corleones discover where the meeting will take place from an informer at the police station. However, Virgil 'The Turk' Sollozzo would surely have known that the police captain had to remain on call 24 hours a day, and in any case, Capt. Mark McCluskey would have given a false location.
During the scene of the meeting between Moe Green and Michael, The boom mic can be seen clearly, as Moe sits down for the first time. A shadow also reflects a hurried movement behind the camera.
When Tom Hagen is trying to convince Sonny not to go to war after Vito Corleone was almost murdered, he states that the Corleone family will be outcasts and all the five families will go after the Corleone family. However, the Corleone family is one of the five families, so he should have said that the other four families will go after the Corleone family.
When an old man sings "A Luna Mezzo 'O Mare" during the wedding celebration, his dentures can be seen coming loose. He re-sets his teeth without missing a note.
(at around 2h 30 mins) At the Don's funeral one of the participants makes the sign of the cross incorrectly. He does Top, Right, Bottom, Left. It's Top, Bottom, Left, Right.
As Michael is walking out of the restaurant, after killing Sollozzo and McCluskey, you can see where he bumps into the camera by the momentary jerk of the picture just as he passes.
When Sonny is beating Carlo, the actor Frank Sivero is watching the fight. Frank Sivero played the young Genco Abbandando in the "back in time" scenes in The Godfather 2.