Fleas -- they're one of the only animals Ben actually doesn't like! Yet, once upon a time, these bloodsucking nuisances were star performers in novelty acts across Europe and, later, North America. But what were they, exactly? Can you really train fleas to do tricks and play instruments? Who even came up with this weird idea? In this episode, the guys welcome special guest and researcher extraordinaire Gabe Luzier to dive into the origin of that bizarre novelty time largely forgot: the flea circus.