After Gus kills his horse to use as a "fort" he shoots 4 attacking Kiowa Indians from their horses, before the gang attacking him retreats to a safe distance. In the rest of the scenes with Gus and the gang interacting and shooting, the dead bodies of those Indians are nowhere to be seen. (Nor are their horses, but they could have run off.)
When the Irish kid falls in the water and is attacked by the snakes, he is bit by one of them on the cheek at the end of chapter one. In chapter two, when his wounds are being investigated, there's not a bite mark on his cheek.
When Wade comes back to the camp from turkey hunting, he finds Luke trying to rape Elmira. He grabs Luke's boots and drags him off, on his belly. The next scene, Wade is holding Luke's boots and the heels are facing out, as they would be if Luke was still on his belly, but in the next scene, Luke is on his back. Again in the next scene, Wade is still holding Luke's boots, belly down, but Luke is still shown on his back.
When Gus rides into camp and tells them that "Blue Duck is in the area", Pea Eye is sitting down in the background eating, and he sets his plate down as he stands up, but in the next shot he is still holding his plate.
Woodrow's horse is equipped with a rifle, scabbard and saddle bags, except they are removed when he is pulling Sean from the river. Then, after the river scene, they are all back on his horse.
When Gus kills his horse to use it as a shield against fire from Blue Duck's men, the horse can clearly still be seen breathing. Additionally, it moves one of its legs in a later scene.
As Blue Duck leads Lorena into Monkey John's camp, we can see a camera shadow on the ground.
After Sean is attacked by the water moccasins, several cowhands jump in the river to pull him out, but none of them are bitten. The last one coming out of the river is just casually walks out.