How do we know what other planets are made of?

How does colour blindness work? How do we know what other planets are made of? Why might a red dye suddenly disappear? Why don't you feel the velocity of a plane for the whole flight? Do mobile phones in crowded spaces expose us to anything dangerous? What causes testicular torsion? How do you avoid getting rats in your car? Where did humans come from? Dr Chris Smith and Clarence Ford have all the answers... Like this podcast? Please help us by supporting the Naked Scientists