A. B. and C. - S1-E3
Revealing mistake: In the fight at the end of the B scenario, Number 6 has a small problem. His pants split open in the back. Fortunately, they somehow manage to mend themselves again.
Revealing mistake: Though the Village isn't supposed to have automobiles (only the little "golf cart" transports), there are several parked cars visible in the shot of Rover floating down to attack the fleeing Villager.
Revealing mistake: At one point, Rover rolls past the Village retirement home, but the film in this sequence was for some reason shown in reverse. Smoke from the building's fireplace is flowing back into the chimney instead of coming out.
Revealing mistake: When Number 6 first enters the bedroom, the light that hangs from the ceiling is moving as though someone has brushed against it. But there's no one else in the room.
Revealing mistake: Number 6 is supposedly flying the helicopter, trying to escape from the Village. There are shadows from the rotor blades crossing his face as he pilots the aircraft. But look closely at the top of the transparent cockpit bubble over his head: you can see the real copter blades - completely stationary and not moving at all.
Revealing mistake: No automobiles are permitted in the Village - ever. Yet in aerial shots, a black car is sitting behind Number 2's residence.
Revealing mistake: After Number 6 has left the Council Chamber for the first time and is heading home, a white car is seen passing by. (00:09:10)
Free for All - S1-E4
Revealing mistake: Stock footage puts Number 6 in two places at once when he grabs the bull-horn and starts shouting at the Villagers to go. There's an inserted shot of the plaza from "Arrival" that includes Number 6 walking through it on his first day in the Village.
Revealing mistake: The "metal" door frame in Number 2's office is bubbling and peeling away from the wall.
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)
Revealing mistake: When Nadia and Number 6 are embracing, many of the reverse-angle shots showing them from behind betray the use of a double for Nadia. Nearly every time the camera angle changes, she is noticeably several inches shorter.
Free for All - S1-E4
Revealing mistake: Though there aren't supposed to be any "normal" automobiles in the Village, there are several visible in this episode, parked in the background. Look closely behind the campaign placards as the golf cart/taxi moves, and behind Number 6 as he leaves the exchange. Several more can be seen behind 6 when the cameraman approaches him.
Free for All - S1-E4
Revealing mistake: Rover flies down from the Green Dome, and briefly reveals his true identity as a weather balloon. His air nipple and guide wires are both showing.
Revealing mistake: When they're "playing" on the swing, Number 6 has his hands on the Butler's shoulders, and the Butler is wearing gloves - yet there's a close-up of someone's bare hand holding the rope.
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: When the red handkerchief is tied to Number 6's hand, Patrick McGoohan's wedding ring is visible in the close-up.
Revealing mistake: Number 6 sets up exercise equipment in the woods and performs several athletic stunts on a bar. In close-up, he's bare handed. In long shots, however, the stunt double becomes apparent because he's wearing gloves.
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: The ultra-secret location of The Village is accidentally revealed when Number 6 drinks his tea. While everything in The Village is supposed to bear only its penny farthing logo, the bottom of the tea cup is emblazoned "Portmeirion Pottery." "The Prisoner" was filmed in the Welsh resort village of Portmeirion.
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