The mouse that craws under the blanket is clearly not the same mouse that is hit with the pan by the Indian woman and then removed from under the blanket.
During the scene in the barn where Aidan Quinn's character was making the 50-cent per acre offer, breath could be seen coming from the Lakota (certainly CGI) but none from the soldiers.
When showing close ups of the dead bodies in the snow after the massacre at Wounded Knee you can clearly see the breathing (nostrils flaring) of the one indian that is supposed to be dead.
The newspaper story being viewed after the Custer battle (Virginia newspaper?) has a dateline of July 3, 1876. The first published account of the event was put out by the Bozeman newspaper (the Times?) on July 4, 1876. Late on July 4, (7:00 p.m.) the Helena newspaper produced a special, extra edition, and at this time, the AP correspondent relayed the material to Salt Lake City, where it was then distributed around the country. The "Virginia" newspaper of the July 3 date could not have contained the story. (Information from searches of archives on the Internet.)
Shaun Johnston as Col. Nelson Miles is shown at the signing of the Fort Laramie Treaty of April 29, 1868 wearing a Civil War Medal and an Indian Wars Medal. The first Civil War Campaign Medal was issued on May 26, 1909. The blue and gray ribbon shown in the film was not in use until August 12, 1913. The first Indian Wars Medal was issued July 15, 1908. The ribbon shown in the film with two dark bands was not in use until 1917.
When Charles Eastman is sitting on the floor, you can clearly see that the soles of his boots are made of man made material with a modern tread design, not the smooth leather soles you would expect to see in the nineteenth century.