At 9:30, the black horse has a prominent white brand on its left rear leg. This is from freeze branding livestock with liquid nitrogen. The freeze brand kills the pigment in the hair follicle, and the hair grows back white. This was not done in this time. Livestock in the mid-1800's would have been branded with a hot brand, which causes a scar where no hair grows - thus reading the brand.
At the beginning of Chapter 2 when the Gatlin gun is used to kill everyone outside of the bank, everyone is dead except the horses. There are tons of people laying dead around the horses, but the horses appeared to be unscathed.
At 51:00, the actor portraying a pastor said the persons killed were all "sired by whores." That's a mistake. The sire is a male, and the dam is a female. He should have said, "they were all out of whores."