When Mattie is emerging from her sleeping area when they are close to Lucky Ned Pepper's hideout, it is evident that she is wearing a form of black nylon tights. Not something you would see in the 1870's.
When Mattie receives the money from Stonehill, the money is clearly 20th century issued US currency, and it is both smaller in size and much less intricate than the currency issued by the federal government in the years following the US Civil War.
At the cabin, while waiting for Ned Pepper, Rooster tells Mattie he lost his eye in the battle of Lone Jack, Missouri, just outside of Kansas City. Kansas City was not given its present name until 1889. Whilst this is technically true for Kansas City, Kansas (although part of the current city had been known unofficially as Kansas City in the past), Kansas City, Missouri was incorporated in 1853.
When Rooster gives LeBoeuf his jacket to cover up the chimney at the dugout where Moon and Quincy were, Le Boeuf throws the jacket over his horse's saddle and sits on top of the jacket. When he emerges on the other side of the river, the jacket is in front of him over the horn of the horse's saddle.
During the hanging scene, the song "Amazing Grace" is being sung. The scene switches to some kids on swings, and the line "How sweet the sound" is sung in the middle of another verse, then the song goes back to the verse that was being sung.
At dinner with Mattie & Chen, Rooster angrily tosses his finished plate atop the stew pot and a chunk of bread tumbles off onto the table. Different size chunks of bread reappear and disappear in subsequent shots.
When Ned and the gang arrive at the dug out he and Mexican Bob ride up through the creek cautiously to check it out. From the overhead view there is just a little area in front of the front door that's shaded but when it switched to a close up of Ned getting down from his horse the whole area is shaded.
When Mattie and Ned get back to the camp Cheney is getting his ribs wounds tended to and sitting with her father's gun in his lap but when he dragged Mattie away from the river he only grabbed his rifle and left the gun where she dropped it.
When Mattie is talking to Ned Pepper while he is watching for Rooster and La Boeuf to appear on the "bald ridge to the north", from a higher rock Harold yells "Hey, Ned!" to alert him to their appearance. At that point Mattie and Ned are facing almost the same way, toward the front, and then Mattie swings around to her right to where Harold is, Ned Pepper swings somewhat to his right, but not far. Then the next shot (a somewhat longer shot) shows Mattie and Ned facing each other, with Mattie looking straight left and Ned straight right.
When Mattie approaches the ferry pulling the horse to join Cogburn and La Boeuf, her shadow indicates the sun's position to the right. Subsequently, all of them are shown from behind, with their shadows indicating the sun's position to the right again.
When Little Blackie finally falls from being rode too hard they are on an upgrade in a mountainous area with several trees all around. Rooster picks Mattie up and begins carrying her off. He then pauses after a few steps as if deciding which way to go and continues on. Next shot is a long one zooming back from them and we can see the whole area has changed to a more level sage brush filled expanse with no trees around.
When Cheney rushes Mattie he throws his rifle down and it's laying to the left of her gun bag. Rooster calls down to her and when she says "Hurry up down here" the rifle is now laying on top of the bag. It's back on the left side of it when Ned and Mexican Bob arrive.
When Mattie and Rooster are looking for a place to set up the ambush on their side she wants to get her revolver and he says "What for? So you can shoot off your foot?" then stops her by grabbing the back of her jacket then leading her off holding her in front of him. Next they are still walking but he's no longer holding her jacket and they have switched positions with him in front and her following him.
After the characters in Fort Smith, Arkansas ride into Indian territory, there are many shots of rocky peaks and snow-covered mountains. There are no such mountains within several hours' automobile drive of Fort Smith. Fort Smith is located in the Arkansas River Valley with the Ozark Mountains to the north and the Ouachita Mountains to the south. Both the Ozarks and the Ouachitas extend into eastern Oklahoma. The Boston Mountains north of town, which are part of the Ozarks, are green, tree-covered mountains. The Winding Stair Mountains in Oklahoma, where much of the action takes place, are in the Ouachitas. They are about 70 highway miles from Fort Smith.
When Chaney is waiting for the ranger and Mattie to return from watching Rooster and Ned's gang shoot it out he decides to pick up a rock and use it on the ranger. One wonders why he didn't just recover the rifle that was tossed aside before.
When they are starting out from their camp Mattie picks up the canteen by the strap and Rooster asks her "where you going with that canteen?". When they switch shots and she answers him that she is going to "wash the sleep from her face of course" the strap is suddenly slung around her shoulder.
When Mattie throws hot water on Chaney and runs he gives chase. Seen from behind she's under or almost under the roof of the little corral as he's coming up. Then when they switch shots to showing it from the front they are farther back again.
When Rooster brings the bodies of the men killed in the shootout at the dugout to Boots Finch, he says that he's looking for Ned Papper. Finch replies, "If you're looking for Little Ned Pepper..." The character's name is "Lucky" Ned Pepper, not "Little".
When Mattie is talking to Ned while they wait for Rooster to get to the bald ridge she's telling him how Hayes is dead too along with the boy that saved his life. Ned answers "I'm happy he done what he done but he should have kept his head and looked out for himself. That goes for your good friend Rooster too." and while he's talking you can see Mattie's eyes glance away 2 or 3 times as if checking her cue cards for her next lines.
In the snake pit, Rooster ties the rope around his waist. Mattie asks him to get her father's gun and when he turns to grab it, the rope is gone. When he turns around to pick up Mattie, the rope is back around his waist.
After La Boeuf succumbs to his head injury and falls off his horse, Rooster turns him over to look at his face. La Boeuf rolls over with his feet crossed. As Rooster and Mattie are riding off and look back at him, his feet are now splayed out.