Revealing mistake: When Sonny is punching Carlo under the spraying fire hydrant, he misses an audible punch by at least six inches. (01:43:30)
Revealing mistake: When McCluskey is lying on the floor inside the restaurant after getting shot dead, he blinks.
Revealing mistake: At the Godfather's funeral, as Al Pacino stands up, you can see a reflection of his mother over on the right of the screen. It's clear in the widescreen video. The same happens when he sits down again. (02:28:25)
Revealing mistake: When Moe Greene is shot through his right eye, the eyeglass is cracked, but has no hole where the bullet penetrated the glass. (02:33:50)
Revealing mistake: When Vito Corleone is walking Johnny Fontane out of his office, he opens the door and you can see an extra walk by and stop, look at the camera and actors, and back up out of the shot. (Mentioned on the commentary). (00:24:30)
Revealing mistake: When Michael and Fredo arrive at the Las Vegas hotel, the actor playing Fredo is replaced by a double who doesn't resemble him even remotely. (02:13:15)
Revealing mistake: After Michael shoots Sollozzo and McCluskey, as he quickly leaves the restaurant and he pushes his way out of the front door, you can see that the shot is jarred because the camera must have been bumped.
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. (01:21:25)
Revealing mistake: When Sollozzo picks up Tom Hagen after killing Luca Brasi, you can easily tell that the snow falling is made of thin plastic.
Revealing mistake: When Michael calls Sonny, after he finds out that his father has been shot, the phone booth he calls from has a broken dial - you can see that the dial is off center and would not work in that condition. (00:45:00)
Revealing mistake: In the kitchen scene where Sonny is talking on the phone one can see that the lower portion of the telephone handset has no internal parts. (00:48:50)
Revealing mistake: When the hooker is lying dead and the senator is sitting on the bed, the sheet moves as she is taking a breath.
Answer: Being a Don for such a long time, Vito has probably seen most every dirty trick used by the other families.