Come In, Your Time Is Up - S8-E4
Revealing mistake: In the very first scene Captain Mainwaring and Sergeant Wilson cast multiple shadows despite supposedly being in bright sunshine.
Revealing mistake: When Stemple and Jason argue on the porch, an electric light bulb is very apparent in the lantern beside the door. (00:41:00)
Revealing mistake: Halfway through the show, the officers get a flat. As Malloy is getting ready to jack up the car, Reed starts using the lug nut wrench to loosen up the nuts. He repeatedly turns the wrench clockwise, which would tighten the nuts.
Aunt Bee's Cruise: Part 1 - S1-E15
Revealing mistake: Aunt Bee is traveling on a cruise ship. The "water" in the background is a painted backdrop which is made all the more obvious by the painted whitecaps.