Fridge Horror
An expression used on the TV Tropes site.
"Fridge" means something you don't think about while watching but do think of later, like when you go to the fridge for a snack.
As I remember the plot, the protagonist, a young Sioux (probably about 18, give or take a year or so) named White Bull, finds that his beloved horse now belongs to Captain Miles Keogh of the Seventh US Cavalry and is unable to get it back.
The great Sioux War breaks out. At the Little Big Horn on June 25, 1876, Custer's battalion is wiped out. Keogh is killed. The horse, Tonka or Comanche, is wounded. White Bull is wounded.
In real history, unmentioned in the movie, the Sioux besiege the troops of Benteen and Reno for the rest of the day. On the next day, the 26th of June, the Sioux besiege the troops of Benteen and Reno. White Bull continues to lie on the battlefield. Detecting General Terry's force, the Sioux abandon the fight and move their great camp south down the Little Big Horn.
On the 27th of June, 1876, General Terry's forces arrive and make contact with Reno and Benteen and find the bodies of Custer's men. They find at least one wounded cavalry horse, Comanche and take him with them when they take Reno's wounded men for medical treatment.
And in the movie they also find White Bull and take him back for medical treatment and he ends up as the attendant in charge of Comanche - the horse that is now the mascot of the 7th Cavalry.
I don't remember if there were any other dead and wounded Sioux and Cheyenne left on Custer Ridge in the movie.
It would be a big anthropological problem if many Sioux bodies were shown on the battlefield, implying that the Sioux left all their dead (and sometimes only wounded) warriors there.
But if White Bull was the only dead or wounded Sioux left lying on the battlefield, there would be another problem. Why was he singled out to not be buried or have his wounds treated?
Imagine a pair of Sioux sightseers:
"Look there's that nice boy White Bull lying there dead!"
"At least he hasn't been scalped yet and thus his spirit has not been destroyed and he can have an afterlife. And he hasn't been mutilated yet so he will be perfectly fit in the afterlife."
"Not yet, but the soldiers might do that when they come, just as those women are doing to that dead soldier there. The nice thing to do would be to take his corpse away and bury it with proper rites and protect it from the soldiers."
"Yes, that would be the good thing to do. Let's go back to our teepee now and leave White Bull's corpse here for the soldiers to do whatever they want to with it."
And if they saw that White Bull was still alive, and he might survive if given proper medical treatment, and the soldiers might kill him or torture him if they found him alive, there could be a similar discussion resulting in a decision not to bother helping White Bull.
And supposedly every Sioux who went sightseeing on Custer Hill and saw White Bull lying dead or wounded also decided to leave him where he was, despite all the other dead and wounded Sioux being taken away.
So what terrible thing by Sioux standards (that we may hope was not very evil by our standards) could White Bull have done off screen that made the other Sioux all despise him so much they would leave him lying dead or wounded, hoping that the soldiers and their Sioux-hating Crow and Arikara scouts would do whatever they wanted to his living or dead body?