Asking how you tell what's real and what isn't sounds like an obvious question. But in this series of six programmes, James Burke shows that the more you think about it the harder it is to answer. After all, what have you got-apart from your five senses - to prove those senses are giving you the real thing? When it comes to deciding what is out there, your brain acts like a private detective. Your senses pick up clues and the brain solves the mystery. Trouble is, it's easier than you think to fool the best private eye in the world.