
One of the things you learn as a skeptic is that sometimes seeing it isn't believing it.
Our group logo was meant to symbolize this idea with an apparent figure visible even if it really isn't there. (the symbol would probably be better if we could have slightly curved the line ends in the punctuated triangle).
Anyway, I came across a great optical illusion, by way of
onegoodmove.org from Phil Plaits blog on bad astronomy at:
http://blogs.discovermagazine.com/badastronomy/2009/06/24/the-blue-and-the-green/The color illusion is so striking, it is hard to believe.
Check it out.
Roy