Other mistake: In the last fight scene, West runs uphill from the cave entering the scene from the most east side of the screen. There is a bad guy on the ground to West's right side as West is running uphill. The villains chase West, but their shot shows them entering the same scene from the middle of the screen with the guy on the ground on their left side.
Deliberate mistake: After Jeremy Pike drops the box in front of the firing squad and it begins to emit smoke, the wind blows the smoke to the right. The actors playing the soldiers in the firing squad then move themselves into the smoke and begin coughing and choking from it.
Factual error: West and Artie are trying to move a cabinet from the wall. A closeup shot shows West's left hand entering from the right side of the shot to press a button that allows a secret panel to open. Unless West twisted his left hand 180°, then him pressing the button as shown is not possible.
Continuity mistake: When Barclay hangs the bone hatchet back in its place, the outline on the wall supposedly left by the item differs significantly from the artifact itself. (Most noticeable is the upper end: the outline has one long curled tip, but the actual hatchet has two short prongs there.) The outline was apparently drawn without the prop, or from a different prop altogether. (00:12:05)
Factual error: Fenlow begins shouting about "one nation, under God, indivisible." This series is set in the 1870s. The Pledge of Allegiance, from which these lines are taken, wasn't written until 1892. And the words "under God" weren't added until 1954. (00:46:55)
Factual error: The coin Artemus hands West is a Morgan silver dollar. It's no coincidence that the actor's thumb covers the date on the coin in the inserted close-up. The series is set during Grant's presidential term in the early 1870s, and Morgan dollars weren't minted until 1878, after Grant had left office. (00:09:40)
Continuity mistake: The bad guys throw an unconscious West down a chute into the ice house. He goes in with his arms at his sides, then slides with his arms above his head, and finally lands with both hands folded over his stomach - all while remaining unconscious. (00:30:30)