We have an illusion that consists of a hollow face of Einstein which seems to be looking at you whether you are looking at the front of it or the back. It’s very impressive. I use it to remind students (and myself) that there is a heck of a lot out there that we still don’t understand, even if we like to pretend otherwise.
The illusion can be purchased from grand-illusions.com, one of the very best sources for all types of illusions.
So when New-Scientist posted a video on how this was being used to test for schizophrenia, I thought perhaps it was time to check it out again (apparently people suffering from schizophrenia don’t notice the effect).