Think about it: the answer to the question "Is it opposite day?" will always be no. It's a head-scratcher. So how do you figure out if it is, in fact, opposite day? We talk to two philosophers who walk us through how questions like these can bend and twist the truth -- and our minds. We learn about the sinister-sounding "Liar Paradox." And we find out that it's not only our brains that use logic, it's used by the machines all around us too. Plus: A brand new mystery sound and an answer to the question: How do erasers erase?