Revealing mistake: When Chingachgook throws his axe in the back of the Huron we see the Huron lying on his stomach with the axe stuck to his back. When the camera moves up leaving the Huron out of sight, we see Chingachgook picking the axe up from a total different angle than the axe stuck to the Huron. (00:19:45)
Deliberate mistake: Rhododendrons, visible in the opening scene and mentioned specifically in the shooting script, do not grow in the Adirondacks.
Continuity mistake: When the Huron chief is talking and Duncan is translating, he is translating faster than the chief can talk. (01:27:00)
Continuity mistake: When Uncas single-handedly attacks Magua's party on the mountain, he shoots an opponent who is filmed falling off the side of the mountain. When the camera cuts back to the fight, you can see him fall down again on the far left (while Uncas is attacking the next one in line).
Audio problem: When Magua complains to the Marquis about not getting his revenge after Colonel Munro's surrender, the Marquis' lips don't match the audio whenever he says Magua's name.