Continuity mistake: Dennis Hopper Says, " these are all his children, man, as far as you can see" and we see a large leaf covering Chef's head and held on with a rubber band. Then when Dennis Hopper says," the man's enlarged my mind . do you know that if is the middle word in life?" there's a different leaf on his head that has much more green in it.
Continuity mistake: Captain Willard and Lance run away from Lieutenant Col. Kilgore and the captain says, "get the f&% outta here". As this happens a helicopter is flying towards the colonel and two soldiers are helping an injured soldier. The camera cuts away for three seconds then back to a wide shot of the colonel again and the helicopter and the injured soldier have disappeared.
Continuity mistake: When Clean first walks up to the sergeant about fuel for the boat there are two posters in the window behind him. The first time we see them their lit up but the second time six seconds later they're not and the blinds behind them haven't been touched. The only thing that's been changed is the stage lighting.