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I have never partaken in any, but I have sat as the sober sitter for others and taking notes (we're all sorta nerdy so that seemed like the thing to do in college).

I've also heard #1 several times. I've also seen people break that rule. Their demeanor changes as something dramatic is hallucinated—the mirrors definitely caused immediate reactions in the people tripping, but that demeanor change was quickly replaced by other hallucinations, interests in the room, etc. The overwhelming consensus was very positive with respect to the whole trips every time I've seen it.