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.
Continuity mistake: Between the time the coded note is tied to the pigeon and the time it is intercepted and handed to Number 2, the handwriting on it changes completely.
Continuity mistake: When he's standing against the wall of the kosho chamber, Number 6 is holding onto the rail, but when the camera reverses angles, he isn't. This goes back and forth several times.
Continuity mistake: During Number 6's visit to the Village Shop, the blue and yellow signs in the window switch places between takes, then return to their original positions.
Continuity mistake: Number 6 recites a classified ad in Spanish to the young woman at the newstand. His phrase contains eight words, but when she reads them back, there are nine.
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)
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.