During "The Longhorns" episode - it was a well known fact that loud or abrupt noises could startle a herd of cattle and cause them to stampede. Yet several times throughout the episode there was a good amount of yelling and hollering between the men as well as other loud noises and gunfire - sometimes at night - and this would not have occurred on an actual cattle drive.
As Louis Verner and Sidney Enderman are driving along in the final episode, the driver's-side rear-view mirror disappears from their Ford pickup whenever a close-up is called for (the holes where it has been unscrewed are quite evident) and reappears in the long shots.
During the "Only the Rocks Live Forever" episode - the same footage of Pasquinel and McKeag in their canoe while Pasquinel is singing a French song is used twice. The first time it is used is when the two leave Lame Beaver's camp right after McKeag meets Clay Basket. The second time - this footage is used again when the two are headed back to Lame Beaver's camp after Pasquinel had just married Lise Bockweiss.