In all forewords Clark Stuart name is spelled Stuart, but in written messages it is written Stewart.
The "mule" Roberto, introduced in Chapter Seven, is actually a small horse which has been made up to look like a mule. I know modern mules have long tail hair, but this movie is set at a time before they were even bred, and the word "mule" meant the same thing as "donkey." Even its braying is fake and has been dubbed.
In Chapter: 1, the same Indian is shot off his horse by two different people.