Some science behind the scenes
The planchette is another variation on the Ouija board. For more details and observations follow the link.
Evidence of Personal Survival from Cross Correspondences – H F Saltmarsh
The planchette, as most people know, is a small heart-shaped board with a pencil, point downwards at one corner, and two little wheels or castors at the others, so that it can move easily over the paper, causing the pencil to leave marks. The operator, or operators, rest a finger lightly upon it, taking care not to direct its movement consciously.
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