Visible crew/equipment: At the surrender of the fort, as the English are marching out, the French general removers his hat. The English Commander, Monroe, says "The fort is yours, Monsieur". Look over his shoulder. In the distant valley you can see what are either two tourist busses or perhaps mobile catering vans.
Revealing mistake: Near the very end of the movie, when Magua has taken Uncas' love interest (Madeleine Stowe's character's sister) and he is taking a path through the mountain, Daniel Day-Lewis runs up a path and brushes against what seems to be a rock. But, the grey coloured "rock" seems to be a prop and moves like a piece of cloth.
Factual error: During the battle over the fort the British shoot a red flare into the sky. The British army learnt of the effectiveness of rocket weapons when fighting in India in the 1790s. In 1804, rockets (developed by Colonel William Congreve) were introduced into British service. The rocket flare was developed around this time (also by Colonel Congreve). This film is set in the 1750s - the British army would not have had rocket flares (source: Taylor, J.W.R (1970). Rockets & Missiles, Hamlyn, London. PP. 6-10).
Factual error: Toward the beginning of the film, when Natty Bumppo first arrives at this friends' cabin, he mentions that he was coming from Schuylerville. This is an anachronism as Schuylerville, NY, was named after the victorious General Schuyler at the Battle of Saratoga in 1779, which would not take place until 20 years after the events of the film. The town would not assume the name for another 50 years after that.
Revealing mistake: After they leave the fort, in the forest glade when the Huron start hollering, the air above the soldiers is very clear. But in the next shot just when the guns start to fire, there is a smoky haze hanging over the forest. Apparently the first attempt to film this scene didn't make it to film and some of the residual smoke was still there when they filmed it the second time.
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.
Visible crew/equipment: When the three Mohicans have leapt through the waterfall, as Uncas and Hawkeye are pulling Chingachgook out of the water, you can see a man climbing a rock behind them, as they move apart slightly.
Continuity mistake: When the Mohicans chase after Magua to save Alice, just after Magua kills Uncas, Alice walks onto the outcropping with Magua. As she stands there you can see rain beginning to fall. A peal of thunder echoes along with the scene. As she turns and leaps off the outcropping we see a shot of her from below showing a nice blue sky and the sun shining.