He makes each swing happen by using a small amount of funds to drive the price down and a larger amount to drive it up. The hyper-reactive lemmings do most of the dirty work for him by accepting the new price he sets and push the trend up or down farther than pirate has funds for.
Whatever the cause, there sure is some absolutely idiotic trading occurring. A good chunk of the sell volume occurred at the price at the bottom when it was dumped followed shortly by buying occurring mostly at prices at the top end when there was the spike. Volatility of 15% in a matter of hours is not sane trading by anyone, if that was the same party pushing both directions.

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https://ferroh.com/chart?t=24hAlso, left completely out of all of this were the other exchanges. The trading at Intersango. BTC=e. BitFloor, CampBX. etc. was minimal. None of them spiked to levels anywhere near what the markets on Mt. Gox did. This is wasteful lunatic selling and buying. It is making great money for anyone that didn't panic though (and who panics nowadays anyway, with no leveraged trading options after Bitcoinica is gone, the exchange rate seems to always return to a certain trajectory).