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 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)
Revealing mistake: When Number 6 finds the black cat outside his house you can see his shadow fall across the painted backdrop of the town behind him. (00:11:39)
Chosen answer: We were never told. In the series finale [Spoiler alert] Number 6 demands an answer to that question, only to be shown his own reflection.
Jean G