Crosseyed Puzzle: Optical Illusions

"e;Crosseyed Puzzle"e; is 30 optical illusions that I invented over the years. It all started when I put a circle on a transparency and focused my eyes through the transparency paper until I saw two circles. This led me to the next step of drawing a face around the now two circles, which gave me the face of a bison. Then came the next step of coming up with a non-abstract picture, which looked to me like a Viking hat. Then I noticed that I didn't have to focus my eyes through the picture to convert the Viking hat into a Bison. Instead, I could print the optical illusion on a plain paper and cross my eyes. Therefore, I came up with the book "e;Crosseyed Puzzle"e;.