In the late 1980s, Marla Sokolowski noticed that if she placed fly larvae on a pile of yeast in a petri dish, some would sit and eat the yeast which they sat upon, while others would move, creating wild trails through the yeast as they ate. What makes some larvae rove around, while others simply sit and eat? And what do these fly larvae have to do with bees? Yehuda Ben-Shahar, assistant professor of biology, returns to continue his discussion on how genes can affect behavior and the various ways the same genes express themselves across species.