Character mistake: The language peculiarity of the series refers to any wheeled vehicle as a "roller." The character "General Tak" accidentally breaks the language rules near the end of the episode and uses the word "car."
Slouching Towards Bethlehem - S2-E8
Revealing mistake: When Kenya is being held at gunpoint the pistol pointed at her has a visible seam running up the grip and the back of the slide. It's a plastic prop.