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What is this volitility?

  1. I noticed that some stocks, like GOOG on Wed May 30 after hours, have one or more large and sudden price movements that don't do anything to the price of the stock in the long term, but in the very short term they can be a huge drop in price, from 499 to 487 in the google case:

    http://finance.google.com/finance?q=goog

    Does anyone know why that happens? Is someone doing that on purpose?