Continuity mistake: When Number 6 is looking for a map in the Village store, the shopkeeper wears a badge with 19 on it. A few shots later, his number has mysteriously changed itself to 56.
Continuity mistake: Number 6 is looking out his window as the maid runs down the stairs. As he watches her, two tables in his apartment change places with each other between takes. A large table with a statue/sculpture on it switches positions with a smaller table on which his lamp and telephone rest.
Continuity mistake: When Number 6 climbs to the top of the bell tower and looks down at the Village, the beach below him changes remarkably between shots. The sequence was obviously shot at different times of day, as the tide is in during much of the scene, but in several intervening shots, the beach sand is completely exposed.
Continuity mistake: When Number 6 observes the stone boat, the tide appears to change from high to low between shots.
Visible crew/equipment: Watch the bottom left corner of the screen when Rover turns around and begins pushing Number 6 away from the helicopter. A film crewmember's head (probably that of the technician operating the weather balloon that played Rover) appears briefly in the shot.
Continuity mistake: When he's trying to escape, Number 6 hides behind a bush with long narrow leaves. But when the camera angle changes to his point of view, the bush now has short broad leaves instead.
Continuity mistake: During the scene with Number 6 and the young woman in the stone boat, Number 6's jacket changes from one shot to the next. The design of the white piping is distinctively different.
Visible crew/equipment: When Number 6 holds up the radio, the camera angle tilts just enough to show us a brief glimpse of the top edge of the studio set.
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