I like illusions.  There’s something about how the brain and eyes work together and how easy it is to fool both.  It turns out that there is so much information in the world that the eyes have to take certain things as a constant.  It is this fact that allows many pictures to fool the eyes into thinking something is there when it really isn’t.  Below you will find some of the more common visual illusions.

1.  This figure is impossible to build in real life, but the eyes do not know that:
imposs2

2.  M.C. Escher used complex variations on this illusion to achieve some wonderful effects like showing representations of people walking in opposite directions, both descending. He also joined staircases into an appearance of infinite ascent/descent:  Look at it for a short amount of time and the stairs will seem to flip.
stair_1

While checking out some visual illusions I came across an audio illusion.  I really couldn’t understand how this works until I heard it.  Play the sound multiple times to hear it “Creep” up in pitch continuously.  Apparently this is known as a “Shepard’s Paradox”.

[kml_flashembed movie="http://www.youtube.com/v/ugriWSmRxcM" width="350" height="288" wmode="transparent" /]