Well it really isn't a "dance" anymore because they used to re rank pages on a monthly basis, now this is a constantly flowing update so there really isn't what their used to be. At times people used to get indexed REALLY high for short periods of time for key phrases, and those of us lucky enough to have had that happen reaped some easy rewards but they were short term 1-2 days if that long. Now I hope that answers your question. Good luck!
hosthop is right. Google hasn't danced for a long time. Previously, during the month, Google sends out robots (spiders) to crawl the web and archive every website it finds. These archived websites will be presented in the next update of the Google index (database). The update process is initiated every 30 days or so, although on some occasions there have been more than 30 days between updates. But now, thanks to the massive computing capability from Google's databases, the update process is a matter in minutes, and Google dance does not exist any more.
The dance used to be where Google processed the data it held in order to rank websites. The result was that rankings changed. However Google has now advanced to the stage where it doesn't need to process that data at certain internvals, it can do it instantly (pretty much).