Invader week! Bugs in our brains, drugs in our waterways, and objects from interstellar space

This week, Claire speaks to ecologist Erinn Richmond from Monash University about pharmaceutical drugs entering our waterways and the effect they may have on the environment; Stu tells us about the interstellar object ʻOumuamua and the chance that it's aliens; and Chris shares the startling discovery that gut bacteria may be living in our brains.