Revealing mistake: In the aerial shot from the helicopter as it overflies the Village, another "real world" car can be spotted parked next to the Green Dome.
Revealing mistake: Watch Curtis' shadow when he and Number 6 have their pistol range competition. The split-screen process cuts his shadow in half.
Revealing mistake: While they ride toward the helicopter, Number 6 and Number 2 have a conversation. Shots of Number 6 are obviously outdoors under windy conditions: his hair is blowing. But every shot of Number 2 has been taken in-studio with a rear-screen projection. His hair isn't moving at all.
Revealing mistake: When Alison enters Number 2's chamber we see a POV shot of Number 6, Number 2 and the doppelgänger facing the camera. If you look closely you can see jittery lines at various points on the screen were the two Number 6's have been poorly overlaid. (00:26:24)
Revealing mistake: Throughout the shooting competition between Number 6 and his Dopplegänger there are numerous shots where both Number 6's are facing the camera and you can see a jittery line running down the middle of the shot where the shots were poorly overlaid.
Revealing mistake: When Number 6 lights up a cigar with the other Number 6 you can see by watching the cigar smoke that there is an exact point on the screen where the cigar smoke cannot travel beyond, revealing that there are two shots being overlaid. (00:16:41)
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