Continuity mistake: Mrs. Butterworth has a sandwich plate in her left hand and her cigarette in her right - until the shot cuts, at which point the cigarette and the sandwiches have instantly changed to the opposite hands.
Continuity mistake: Number 6 pushes the dead body out into the surf. In close-ups, the body is still very near the shore. But in long shots, it is much further out. (00:28:30)
Continuity mistake: At the end, the computer produces a print-out with two lines of type at the bottom, then pauses. In the next shot, when it starts printing again, the two lines have disappeared.
Continuity mistake: When Number 6 falls on the beach, the sand under him is wet. In the next shot, it is obviously dry.
Continuity mistake: Number 6 gets into the buggy with the hypnotised woman (Number 8, I think) however, when seen from behind, as the vehicle drives away, there is now only one person in the buggy. (00:29:47)
Continuity mistake: On the beach, the Queen is sitting on a large rock and conversing with Number 6. Then she's seen standing down near the water. After an abrupt cut, she's back on the rock without enough time to have moved there.
Continuity mistake: Number 39 is writing notes on the word association test in her notebook. When the shot cuts to a close-up, however, the notebook disappears from her hands. It's back a short time later.
Continuity mistake: At the start of the chess match, a man holding a stick climbs the ladder behind the Queen and settles in to watch. As Number 6 and the Queen converse throughout the game, however, both the ladder and the man have vanished. They both reappear behind the Queen as the game is ending.
Continuity mistake: Rover herds the boat back to the beach, and several people who were aboard minutes before (some of them unconscious) have somehow disappeared from its decks.
Continuity mistake: Number 6 is taking notes on the Village inhabitants, trying to determine which of them are prisoners and which are keepers. Next to the pond, he's observing Number 62. But on his notepad, he crosses out Number 8.
Continuity mistake: At the end of the chess match, the player wearing blue comes down off his platform, descending the ladder and walking onto the field. In the very next shot, as his opponent approaches Number 6, the man in blue is in the background, once again coming down the same ladder. He didn't have time to climb it again.
Continuity mistake: In the opening shots, the Village center is shown without the giant chessboard set up. In the very next shot, it is suddenly fully laid out on the green.
Continuity mistake: When the command "Knight to Queen's Bishop Three" is given, it's not a knight that moves, but a pawn. In the next long shot, though, Queen's Bishop Three isn't occupied by anyone, pawn or otherwise.
Continuity mistake: When Number 6 is setting up his antenna, there's a woman on the beach in the background in a blue bathing suit. Between takes, her beach umbrella disappears.
Continuity mistake: When Number 6 writes the coded message he uses black ink, after Number 2 intercepts the message it changes to blue ink. (00:37:24 - 00:38:30)
Continuity mistake: When Number 2 is shouting at Number 14, calling him a traitor, Number 2's long strands of hair are flying all over his head. In the very next shot, though, his hair has nicely combed itself and he's well-groomed again.
Continuity mistake: The new supervisor holds a clipboard in both hands up near his chest. When the shot cuts, he's abruptly holding it in one hand down at his thigh.
Continuity mistake: Number 6 points the mirror out to sea and tries to send a signal. But when we see him from the POV of the security camera, he's pointing the signal mirror toward the Village instead. When the shot cuts back to him on the beach, the buildings are again behind him and he's facing seaward again.
Continuity mistake: During their kosho match, Number 6 ends up dangling Number 14 over the water. In the first shot, he's holding the man with his left hand. In the next, he's using his right hand.
Continuity mistake: Just before the fight begins on the roadway, Number 6, in full shot, steps off the grass and onto the road. But the next close-up of him shows him on the grass again.
Answer: It's even more obvious than you think, you know who number 1 is in the very first episode. When 2 replies to the question "who is #1?" Change the way he answers from you are number one (in the monotone or accented answer to, "You are, number 6. The comma gives you the answer. #6 is #1. It's the tone of the answer.