It's an open question, though compelling new research is lending credence those who argue that they do. Neurobiologist (and recent Daily Show guest) Sharon Moalem outlines the theory in his new book, Survival of the Sickest. There's a nasty little parasite named Toxoplasma gondii found in cat poo -- and long known to be mildly toxic to small children and pregnant women -- which when eaten by cat prey like rats and mice actually affects a behavioral change; it makes the rodents less afraid of cats, which in turn makes it easier for cats to catch them. So what's the connection to schizophrenia? Moalem hypothesizes:

"People with schizophrenia have higher rates of infection with toxoplasmosis. Which doesn't prove a causality, because the higher rates of infection may also be due to poor hygiene or spending time institutionalized. But the smoking gun for me has to do with toxoplasmosis having the ability to change another animals behavior as in the case of mice. I believe toxoplasmosis may be an added trigger not unlike drug use to make someone who's already susceptible to schizophrenia all the more likely to get sick."

So cat feces might be more than just toxic to kids -- it might be increasing the chances that they'll develop schizophrenia later in life. Crazy, huh?