Visible crew/equipment: In the opening scene, when the TV turns on as the news comes up, you can see a man with a white shirt in the reflection of the TV. (00:01:50)
Visible crew/equipment: When Marty is riding past the cafe on his skateboard and all the chicks are waving at him, you can see the reflection of the camera lorry and crew behind him. (00:06:25)
Visible crew/equipment: In the scene in the beginning where Marty meets up with Doc for the first time, Doc shows Marty how the DeLorean works with the remote control with Einstein in the car. In the shot that switches to see Doc put the car in reverse on the remote control, you can clearly see a crew member manually steering the car in a dog costume (You can even see his hands turning the steering wheel). (00:20:30)
Visible crew/equipment: When Marty asks if the time machine is nuclear, a boom microphone is visible in the right windows of Doc's van. (00:26:28)
Visible crew/equipment: A boom mic reflection is visible on the vent window of Doc's van when Marty asks him if the plutonium was ripped off. (00:26:35)
Visible crew/equipment: When Marty arrives at the 1950's town and is about to be run over by a green car, the whole filming crew is reflected on its door. (00:35:40)
Visible crew/equipment: A boom mic pole is reflected in the glass near Doc after Lorraine and her friends run past him in the school hallway. (00:57:40)
Visible crew/equipment: When Doc Brown loses his footing on the clock tower as it begins to toll, in the next shot, when he swings about towards the clock the thin black stunt cable attached to his waist, that leads around the neck of the statue, is visible. Do not confuse it with the thick silver electric cable Doc is holding. (01:35:25)
Visible crew/equipment: When the clock tower ledge breaks, Doc Brown slips and loses his grip on the electric cable. In the next shot the stunt wire pulling the thick electric cable towards Doc's pants is visible. (01:37:50)
Visible crew/equipment: At the end of BTTF they all pile into the DeLorean which reverses up to the camera where the matte box and what looks like the top of the cinematographer's head are reflected in the chrome number plate. (01:46:50)
Chosen answer: I think that is *exactly* what he is thinking. He realizes that by standing up to Biff, George may have irrevocably changed his personal future, and therefore affected Marty's future as well. This is exactly the sort of thing Doc was so eager to prevent by refusing to hear any information about the future.
Phil C.