The flare launched from Fort William Henry, during the bombardment scene was equipped with a parachute to provide longer use. This type of flare was not invented until shortly before the First World War.
The bars of the cell in Fort William Henry, in which Hawkeye was detained, were deformed reinforcing rod (rebar). Reinforcing rod was not used in construction until at least 1848, but deformed rod requires specialized rolling machinery which did not exist at that time.
During the scene at Fort William Henry where the colonials are arguing with General Munro about releasing them to go back to their farms, Cora is shown standing in a doorway. In the first scene where she is first shown, the doorway is over her left shoulder. In the subsequent scene, the doorway is over her right shoulder and she ultimately exits through this doorway.
When the party going to Fort William Henry is attacked, Alice's hair is pinned up in a complex pattern. However, a few minutes later her hair is completely down and there is no evidence that it was ever done up at all.
As the British Army is retreating from Fort William-Henry, Magua ambushes the British. At one point in the battle, Major Duncan Heyward is commanding a small group of British soldiers. Most of them get killed, and he begins to run away. The bayonet on his rifle disappears soon after he shoots one of the Indians.
After Chingachook delivers the final blow that kills Magua the first shot is of him from the waist up. He begins to raise his right foot to disengage Magua's body from the war club blade. The next shot shows his left foot raised and disengaging Magua's body from the blade of the club.
The French are seen lighting the bomb fuses in their mortars and then firing the mortars, when by the Seven Years' War it was discovered that the flash was sufficient to ignite the fuse on a bomb (and indeed safer).
Gray rock-textured canvas, presumably covering modern trail signs or graffiti, is clearly visible in final scenes. Hawkeye bumps a canvas while running through underpass, and a larger portion is visible as he returns to embrace Cora after Magua's death.
Just after they send their canoes down the waterfall and right before going into the cave, the water on the left edge of the waterfall vanishes and reappears as it is falling. Patches of the water appear to have been digitally cut out.
When Major Heyward and Cora Munro first meet and discuss marriage, there is a large sheet on a washing line flapping violently in the wind. However, none of the three characters in this scene is remotely affected by the wind.