She Wore a Yellow Ribbon (1949)

Plot hole: Immediately before the attack on Pony-That-Walks' village Capt. Brittles states that it's 12 minutes to midnight,and orders the attack. The attack is a surprise attack, yet all the warriors pile out of their tipi's fully clothed, painted and with their eagle feathers braided into their hair.

Factual error: In the beginning of the movie there is a shot of the flag being raised over Fort Stark and the sound of a bugle is playing. The bugler is playing "Retreat" which is only played when the flag is coming down; he should be playing "To The Colors".

Factual error: In the very beginning of the movie, the narrator says, "Pony Express riders know that one more such attack (referring to the Custer Massacre) would mean a hundred years before another wagon train crosses the prairie." Then they show a Pony Express rider supposedly carrying the news. But the Custer massacre happened in June of 1876, and the Pony Express went out of business in 1861.

Captain Nathan Brittles: I don't know where you got your brains, Sergeant - God must have given you that pair of eyes. They're Arapahos, all right. Headin' the same way we are. Now why would they be movin' on Sudrow's Wells, Sergeant? Answer me that.
Sgt. Tyree: My mother didn't raise any sons to be makin' guesses in front of Yankee captains.

Captain Nathan Brittles: Give 'em a wide berth. Mr Cohill, past Sudrow's Wells by way of Twin Forks.
Lt. Flint Cohill: We'll lose half a day, sir.
2nd Lt. Ross Penell: The ladies will miss their stage, sir.
Captain Nathan Brittles: Would you rather have them miss their scalps, sir?

Jenkins: Sure got a hankerin' for some buffalo meat.
Trooper Cliff: Me too. Ain't never had none.
Trooper: Beans is safer. Mark my words, they'll be Injuns around that herd thick as flies.