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A rattleback (also known as a celt or a wobblestone) is a type of spinning top that will spin in one direction, but when you spin it the other way it will slow down until it stops, wobbling along its length, and will then spin in the opposite direction. Originally seen as mysterious, they are now regarded as an interesting piece of physics. One of the original papers explaining how they work was presented at the Royal Society in London in 1988.
