Rattleback - Breaking the Laws of Physics? (Walter Lewin rotation experiment)

This quite special top is called a rattleback, or celt. See Wikipedia : http://en.wikipedia.org/wiki/Rattleback

I quote : "The spin-reversal motion follows from the growth of instabilities on the other rotation axes, that are rolling (on the main axis) and pitching (on the crosswise axis). (...) The amplified mode will differ depending on the spin direction, which explains the rattleback's asymmetrical behavior. Depending on whether it is rather a pitching or rolling instability that dominates, the growth rate will be very high or quite low."

You can find some for sale or even build your own : http://www.iop.org/EJ/abstract/0143-0807/11/1/112