Many of the cast members met with specialists and psychologists to learn and understand their characters' situations.
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In Episode 1 (and Tape 1, Side A) Hannah says that there are 13 sides to every story, and that this is the reason for making 13 tapes. However, at the time she recorded the first tape, she had only planned on making 12, which she reveals in Episode 12. She didn't intend to record a conversation with Mr. Porter until days later.