Such is the case with T. gondii. It sexually reproduces only in the intestines of cats yet can maintain itself indefinitely in any warm-blooded animal. Infected cats shed millions of their oocysts in their feces. Taken up by all kinds of animals, including dogs, rodents and humans, they infect muscle and the brain to escape attacks by the host’s immune system. Hidden away, they remain dormant as cysts, surrounding themselves with a tough cell wall. Yet this quiet stage of infection, called toxoplasmosis, is deceptive. Violating all rules of good hospitality, these invaders make the host’s brain do things counterproductive to its own survival.