It's a common parasite carried by cats. It infects mice, then causes the mice to be attracted to the smell of cat pee. The mice loose their fear of cats and actively seek them out. Cats, naturally, don't pass up a free meal and eat the infected mice, getting infected themselves in the process. The good news is toxoplasmosis is only transmitted through cat feces and causes no harm to the cat or human that may be infected. It only makes rodents suicidaly attracted to cats and cat owners are less likely to be botherd by the smell of cat pee after being infected. There is a theory that the majority of cat owners are already infected and extreme cases combined with existing mental illnesses is what causes crazy cat ladies to be a thing.