It has long been known that our bodies are really a mishmash of many different organisms. Microbes in your gut can produce neurotransmitters that alter your mood; some scientists have even proposed that the microbes may sway your appetite, so that you crave their favourite food. An infection of a parasite called Toxoplasma gondii, meanwhile, might just lead you to your death. In nature, the microbe warps rats’ brains so that they are attracted to cats, which will then offer a cosy home for it to reproduce. But humans can be infected and subjected to the same kind of mind control too: the microbe seems to make someone risky, and increases the chance they will suffer from schizophrenia or suicidal depression. Now it is time to start listening to these voices.