Optical illusions
There are a lot of interesting optical illusions “shown here”:http://www.ritsumei.ac.jp/~akitaoka/saishin-e.html. It also gives details of some places to do further reading on why our brain perceives these images in a particular way. Some of them are rather bizarre, and begs the question of how visual perception *really* works. Time to do some reading, I guess.