the vanishing head illusion something we did in biology in Germany to show the blind spot of the eye it works because there is a point in our sight for each eye on which we are completly blind. It is connnected to the anatomie of our eye because that spot is where the nervcells lead to our brain, therefore there cant be any light receptores located at that point.

here the video:
http://www.youtube.com/watch?v=O7jpJ12lBjg