Being a Graphic Designer I get all kinds of weird design request from my peps. My one friend who I'm designing a band logo for wanted a trippy shirt design. I saw this optical illusion once on the web but I couldn't remember where I saw it. So I re-drew it from memory. It works for me. It's not as cool as Oddballs but it does mess with you. The lines are all parallel to each other, you can check with a ruler.