Do Not Forsake Me Oh My Darling - S1-E13
Revealing mistake: When No. 6 is putting the 4 slides together to get the location information for Seltzman, as the slides are dropped into the top of the projector, they drop down the screen. However, a projector inverts slides, so they should slide up from the bottom. Also, when the last slide is dropped in, the final letters fade into view and not slide down as would be expected. (00:33:30)
Chosen answer: We're led to believe Rover is some kind of robot in the series. According to books on the show, Patrick McGoohan was looking for an unusual guardian for the Village, looked up at the sky, and saw a weather balloon, which was what Rover was.
Captain Defenestrator