http://www.fazed.net/video/view/?id=736
'hollow head illusion' and below is the spinning silhouette illusion. The trick with the spinning silhouette is to look directly at the shadow of the dancers foot as it spins, and your brain sets the dancer spinning in the opposite direction. Can take a while for the illusion to work, took me about 5 minutes before my brain gave in.
http://www.moillusions.com/2007/06/s...-illusion.html
these illusions are good reminders that things arent always as they seem, and its something we need to keep an open mind about in the cockpit.