July Johnson enters a room to visit Elmira, who is sick in bed. He closes the door behind him, and the audio is the sound of a door solidly closing shut. But look closely, and you will see that the door did not close shut, but in fact "bounced" open, and remains a few inches ajar with some light coming in from the outside.
Preparing to hang Jake and the Suggs brothers, Call orders them to get their boots off and we see Dan stoop to comply, yet when it comes time to hang Jake, Jake spurs his horse before Gus can slap it, and there's a closeup of Jake's spur and boot.
Just before Deets (Danny Glover) dies from being speared by an Indian, he's shown with his eyes gradually closing to a slit. After a cut away and return to show Deets' face again, his eyes are wide open.
Cavalry "Captain" Weaver wears a uniform with the double-breasted three times, three button pattern of a major general. Even if the captain had been wearing a frock coat as he is in the film, it would have been single-breasted without the three separate groupings of buttons.
After crossing over 80 miles through the "Badlands" without water, the cattle don't start running until the river is in view. In truth, thirsty cattle can smell water for many miles, and would have stampeded towards the water much earlier than depicted in the movie.
When the army is trying to take the horse from Dish, the Captain mentions that his horses were tired of chasing Red Cloud. "Red Cloud's War" lasted from 1865 until the signing of the Treaty at Fort Laramie in 1868. In the second episode, Captain McCrea mentions upon leaving the saloon where he beats up the bartender that they would have been remembered if they had been killed by the Comanche's like Custer had by the Sioux. The Battle of the Little Big Horn where Custer was killed was in 1876, eight years after the Treaty of Laramie that concluded Red Cloud's War.