Ouija Board
The Ouija board is a lettered board and a sliding planchette, sold as a parlor game since 1890 and blamed for a century of trouble since. Science has a clean mechanism — the ideomotor effect, tiny unconscious muscle movements — and it genuinely explains the moving planchette. What it explains less well are the sessions readers file here: names nobody at the table knew, answers in a dead grandmother's spelling mistakes, and the classic ending — the planchette carving to GOODBYE by itself. Half the jury votes fake. The other half unplugs their attic.
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