At the onset of this episode when Lucas and Mark are captured by the vaqueros, during their capture, the main vaquero grabs Lucas' rifle away from him and ultimately hits Lucas on the left side of his throat with the stock of the rifle. Lucas falls to the ground, grimacing in pain. A few scenes later, when Lucas is struggling, it's the right side of Lucas' throat that is very bruised and injured, not the left side.
The guitar players strumming doesn't sync with the music heard.
Lucas and Mark are in Mexico 150 miles from the Rio Grande. Most outdoor scenes in The Vaqueros (#4.1) have Joshua trees. Joshua trees (yucca plants) have a limited range mostly in California and western Arizona. They should be hundreds of miles from the nearest Joshua tree.
When Lucas busts into the saloon to grab his gun and kills the Vaqueros he uncharacteristically shoots wildly. Some of his shots look like they would have hit above the bar.