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 can make the two spirals appear to unwind, yet however many times you repeat the action, the two spirals never come apart.From another discussion:
For those who still don't get it: the guy is only moving his hands along the rod. He's also rotating the rod at the same time so that the part of the rod that's "coming out" of his hand is also at the same angle, to create the illusion that he's firmly holding the "rods" with his fingers.