Velvet hand illusion
This is a very bizarre tactile illusion. Put you hands either side of a series of wires, and pull them across, your other hand will suddenly feel smoother than velvet.
This is a very effective illusion, and as long as the text introduces it correctly just about everyone will experience it, and visitors love it.
Your skin senses roughness by moving across a surface and detecting the amount of vibration it causes. When you use this exhibit, your senses are fooled into thinking your hands are moving past one another because the wires are moving, but your hands are stationary relative to one another, producing no vibrations, which you interpret as being extremely smooth.
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