Revealing mistake: As Captain Willard takes his second swing at Colonel Kurtz there is a "spark" superimposed against the wall behind his head, which is to depict the contact point of the blade to the wall. However, the blade is actually resting on the Colonel's back, nearly a foot away at that time.
Revealing mistake: A Medevac helicopter lands in the courtyard and later explodes when a Vietnamese woman throws a grenade into it. The copter that lands is not the one that explodes. The front of the helicopter that blows up is older and beat up and the window on the pilot's door does not have any green sun shade on top as the other chopper had when it landed. The one that explodes is also on a platform that collapses as it blows up.