Early in the movie during Tom and Mary's conversation on the train, when the camera is on Tom, steam/smoke is visible passing by the window beside them, but not when the camera is on Mary.
During the skirmish between the cavalry and the Indians in the desert, the sky alternates between clear blue sky to overcast cloudy sky.
1st Sgt. Rutledge says the Apache are Mescalero. This story is set in Arizona and the Mescalero are and have always been a New Mexico people.
"Poor little girl." When the German-speaking doctor sees the corpse of the young woman, he says "arme kleine Maedchen." It should be either "armes kleines Maedchen" or "das arme kleine Maedchen." He is either using feminine endings with a neuter noun, or weak neuter endings without a strong neuter article. No educated German would make this mistake.
Trial witnesses are supposed to place the left hand on the Bible and raise the right hand to swear, but some of the witnesses do the opposite, and Sgt. Rutledge does both with his right hand.
Cordelia testifies to hearing two shots from Major Dabney's quarters on the night of the murders. But Major Dabney's small revolver has been fired twice, and Sergeant Rutledge has been wounded twice, as confirmed by Lieutenant Cantrell's examination of Rutledge, "But this wasn't Apaches, not two small-caliber bullet wounds." Since Dr. Eckner found that Dabney had been killed by another shot from a large caliber service gun, Cordelia should have heard three shots.
Cordelia states she heard two shots and then when she opens the window there is another single shot which makes three in total.
During defense counsel's testimony the lieutenant testifies that he and his men "arrived at Spindle Station shortly after dawn". Judging by the shadows being cast while at the gate it looks like the time would more likely be 10 or 11 a.m. The scene changes to the front of the station and the shadows of the posts are much longer suggesting earlier morning or late afternoon - neither of which are consistent with dawn.
Note that the station scenes are all filmed on an interior set so the shade and lighting are artificial.
When the troop is settling in for the night and sings "Captain Buffalo" there is a shot of Rutledge standing watch. The rafters of the soundstage are visible in the upper right corner.
When Lt. Cantrell is holding a picture of the young Miss Lucy Dabney over her dead body, he moves the picture out of camera frame, and you can see her moving her right eyelid.
When everyone is inside Spindle Station and the 1st Sergeant is already in handcuffs Lt. Cantrell orders the men to search Sgt. Rutledge, etc. then barks a command to "tie him up". There's no binding at the wrists (only the cuffs) and Rutledge walks out without his ankles bound. Not a piece of rope in sight.
In the train car during the first flashback when Tom and Mary are talking, the ride is as smooth as silk as the car is not rocking and no item inside shows any movement whatsoever.
When the Colonel has the courtroom cleared of spectators the ultimate guilty party remains seated although he is not a witness and doesn't testify until called by the Colonel after the formal proceedings are over. There is no logical reason he would have remained when everyone else except actual witnesses was removed.
At around 116 minutes, in an 11-second sequence, Rutledge sees through his binoculars: first, hostiles and a captive on horseback; second, just the hostiles; and third the hostiles and the captive. How the binoculars changed views needs explanation.
Lt. Cantrell and Mary are seated at a table with a red and white checkered table cloth while aboard the train. Light reflects off the table cloth as does the color of Mary's dress when she stands.
The US Cavalry officer saber shown throughout the movie appears to be the straight blade, double edge M1913 Patton style saber which wasn't adapted by the military until 1913. Since the movie appears to be set before 1900, the cavalry would still be using the swept back single edge Model 1860 Light Cavalry saber.
Lucy greets her neighbors and the men serving in the store by saying "Hi" to each of them. This word would not commonly be used as a greeting until more than a generation later, and would never have been considered a proper way for a girl to greet a lady old enough to be her grandmother.
The railroad in the first flashback is named the "Tombstone & Gila" railroad. This film is set in 1881 and Tombstone would not have any rail service until 1903.
Sergeant Rutledge uses binoculars to view the Apaches across the river and there is a very unique rock structure on the cliff Benin's him. In a later scene the Apaches on the other side of the river are firing across the river on the troops and this same unique rock formation is now behind the Apaches on the other side of the river.
When Dr. Eckner testifies as to the rape/murder, his testimony is shown in flashback and concludes with a conversation between Skidmore and Cantrell that took place outside the building. As the doctor remained inside, he could not possibly have heard it.
When Rutledge says that he pleads "not guilty," the soldiers are shocked. However, if they did not know that he intended to so plead, they would not have summoned a defense attorney. Further, at a court martial a defendant is always considered innocent until proven guilty.
Early in the trial the senior officer has the courtroom cleared of spectators. Then later, after a recess and just before the conclusion, all the spectators are inexplicably back in the courtroom so they can react to the proceedings.
Cantrell explains that the "Buffalo Soldiers" were so named because when first seen by the Native Americans, the Natives mistook their woolly coats for those of a buffalo. In truth, it was the "nappy" hair of the Black soldiers that lead the Natives to dub the unit as "Buffalo Soldiers," but Cantrell could have been misinformed.
During Cantrell's speech in which he brings up the evidence of the necklace, he bobbles a line by saying "being capable of tipped" instead of "capable of being tipped".
In the train car, Owens has a steaming metal pot of chow cooking on the pot-bellied stove. He grabs the metal handle of the steaming hot pot and lifts it off the stove with his bare hand without burning himself. Of course it is not hot at all as the "steam" is being provided by pieces of dry ice in water.