Science is a powerful fact-finding tool -- but how does it work? In this second installment in our series "Prove It: How to find the facts," we look to the past for answers. We find out how a snake heart helped get rid of an old idea about blood and how failed experiments are just as important as successful ones (bye bye, luminiferous ether). And we'll hear from scientists working today about how curiosity is at the heart of science. All this plus a new Mystery Sound and snail-rific Moment of Um. Today’s episode is sponsored by Build-a-Bear Workshop (buildabear.com), Ozobot (ozobot.com/brains) and Bombas (bombas.com/brains) and you can support Brains On at brainson.org/donate. See omnystudio.com/listener for privacy information.