Reader comment: David says: Here's a page with 57 optical illusions and visual phenomena. The purple dot illusion is also on there, but figured other fellow BB readers would be longing for more."
Mark Frauenfelder is the founder of Boing Boing and the editor-in-chief of MAKE and Cool Tools. Twitter: @frauenfelder. His new book is Maker Dad: Lunch Box Guitars, Antigravity Jars, and 22 Other Incredibly Cool Father-Daughter DIY Projects