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)BillyBlake
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.