Mephisto Spiral

An optical illusion, or a magic trick - take your pick! We first came across this many years ago, but it is hard to find, and few people have seen it. It looks like 2 interlocking wire spirals. In your hands, the two spirals seem to wind together or wind apart, completely effortlessly. However when you hand the Mephisto Spiral over to someone else, they find that they cannot replicate the action - the two wire spirals are completely rigid. Alternatively, by simply moving your hands in one direction, you c