How do we rationally assess risk? Following a terrible series of horrifying air travel disasters, reasonable people begin to question what we consider to be "safe." But should we?    To answer this question, our host Josh Zepps is joined by David Ropeik, an international consultant and expert on the subject of risk perception and communication, and author of Risk: A Practical Guide for Deciding Whats Really Safe and Whats Really Dangerous in the World Around You and How Risky Is It, Really?: Why Our Fears Don't Always Match the Facts.    Ropeik discusses how human beings perceive danger versus mathematical probabilities, how fear and optimism affect our perception, and how it might be a good idea to be "gentle" with the word "rational" when it comes to the subject risk.