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Sisyphus was very clever. Explain how he tricked Hades, so that he could escape Tartarus.
He watched Hades take out a heavy set of chains. Sisyphus saw this as his opportunity. He said "Oh mighty King, I've never seen chains like that before, perhaps you can show me how they work. Hades said it was quite simple, you just wrap them around your wrist like this, and before he realized what he had done, Hades had chained himself in place. Zeus then escaped Tartarus. But not for long.