Continuity mistake: When Luca Brasi is practicing his speech he is wearing a square faced watch. When he gives his speech to the godfather he's wearing a round faced watch.
Continuity mistake: When Sonny is shot at the toll booth the front windshield is torn apart by bullets yet when the bodyguards arrive thirty seconds later, the windshield is intact. (01:53:20)
Continuity mistake: After Michael shoots Sollozzo in the head, he turns to McCluskey and shoots him in the throat and then in the head. But in the long shot, before he shoots McCluskey in the head, you already can see the hole in the forehead. (01:25:15)
Continuity mistake: When Tom Hagen is meeting with Jack Woltz, the server fills Tom's wine glass twice within a split second. (00:29:20)
Continuity mistake: When they're all having a meal in Sicily, watch behind Appollonia. Two people, one in red, one in white, walk past in the same direction twice - once in a wide shot, and once in a close-up of Appollonia. (01:40:35)
Continuity mistake: When Michael and Kay are eating lasagna during the wedding, Kay is smoking a cigarette. But depending on the shot, that cigarette disappears from her hand, then reappears. (00:13:25)
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. (00:58:00)
Continuity mistake: When Marlon Brando is gunned down at the fruit stand, he drops the bag of fruit he just bought. However, when he's collapsing against the car, the bag of fruit is now on the hood of the car. (00:43:05)
Continuity mistake: When Clemenza knocks at the door Sonny gets a gun from a drawer and puts it in his belt. When he pushes Clemenza the gun disappears, but it's back a moment later. As the shot where the gun disappears is uncut the gun must have slipped down his pants. (00:46:20)
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. (00:52:55)
Continuity mistake: When Michael is talking to Moe Green in Las Vegas, he takes his cigarettes out of his pocket twice in two seconds. (02:17:15)
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. (00:43:10)
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. (00:54:40)
Continuity mistake: When the Godfather tells Tom that he is going to California that night, his glass switches from his left to his right hand. (00:24:20)
Continuity mistake: Right before Sonny collapses his jacket is covered with with blood. When he is shot at while he is lying on the ground the amount of blood has gone down substantially. (01:52:55)
Continuity mistake: When the baker is meeting with Don Corleone about keeping Enzo in the country, he's holding a shot glass in one hand, and a thin cigar in the other. When he reaches out to clasp the Don's hands in gratitude, the items are gone. A split second later, they're back. (00:11:20)
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. (01:09:30)
Continuity mistake: During the strangulation of Luca Brasi, two mistakes occur between the front and side shots of him dying. First the knife in his hand disappears; second his head goes from being about a foot under the counter to about 6 inches over. (00:43:30)
Continuity mistake: When Barzini gets shot in the back we see a lot of blood and other matter pouring out. When he rolls down the steps his coat is intact again. (02:34:25)
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. (00:06:00)
Suggested correction: Look again, the broken windows you are seeing are from the side windows, the windscreen was shot out entirely.
The screenshot shows the windscreen is intact after being shot out.