Optical Illusions

Julian Beever creates sidewalk art that looks three-dimensional when viewed from a certain angle. Here's one of his creations:

More pictures of his stuff are available here and here. It's pretty hard to tell that these are two-dimensional drawings. Oh, senses! Why won't you stop deceiving me?!?

ALSO: One response to computer simulation skeptical scenarios like the Matrix is to say that the computer simulation just is our reality. That's what we'd be referring to, after all. When someone stuck in a computer simulation says 'clock,' she's referring to the computer simulation of a clock. Here's an article on that response.