Revealing mistake: After Jon Voight has killed the mountain man and has tied a rock to his body so he can dump him into the river, the "dead" man takes at least two deep breaths right before he is rolled off the rock and into the water. In that same shot where you see his chest heave and him noticeably breathing, he also flinches and moves the pinky finger of his left hand.
Continuity mistake: In the scene where Lewis and Ed are in the canoe after setting up camp and Lewis is bowfishing while Ed is drinking beer, Lewis shoots a trout. You can clearly see the arrow hit the fish just behind its head in a close-up shot. When Lewis pulls the fish in, the arrow is through the middle of the fish's body.
Revealing mistake: In the famous "dueling banjos" scene I noticed several errors revealing that the actors are not really playing their instruments. This happens throughout the whole scene. The banjo player is using a different picking technique than would be necessary to create the music heard. His finger patterns on the fretboard don't match the sounds heard. The guitar player strums when you hear individually picked strings and visa versa. Again, his fretboard fingering does not match the music heard.
Factual error: In the beginning of the film the setting is very late summer or early fall as evidenced by the reference to getting back home in time to watch the football game on Sunday. Yet the deer that Ed shoots at is in the early stages of antler growth that appears to be more typical of late spring or early summer. The deer also appears to be some exotic species, not one of the whitetails that are native to Georgia.
Continuity mistake: When Ed loses control of the canoe and is trapped between two rocks, the other canoe strikes his and breaks it in half sending him and all of the contents of the boat, including his hunting bow, over the falls. Ed tumbles down the falls with nothing in his hands. In fact at one point he tries to scramble out of the water using both hands in the attempt. Yet two shots later he suddenly has his hunting bow in his hands. (01:02:05 - 01:02:50)
Revealing mistake: The entire sequence of Voight climbing the cliff face is shot day for night, meaning the scene is supposed to take place during the night but was shot during the day. This is painfully obvious by the amount of contrast in the scenes we see sky (and the colored shots when he is on top of the cliff). When the camera pans up, it is a blue sky day but the scene takes place at night.manthabeat
Revealing mistake: When Voight goes over the waterfall just after his canoe breaks in two, it is a stuntman.