Tiberius wrote:

I always figured that the holodeck works like a replicator if you actually carry something out (like the paper), but if you don't, it vanishes (like the book that Picard or whoever tossed out in "Ship in a Bottle".
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I like that explanation, but it still doesn't cover Wesley's snowball, which crosses the plane intact. Ultimately, they muddled the science on that one often