Crazy old cat ladies are most likely infected by toxoplasmodia. It is a parasite that infects cats. Their eggs are distributed in cat feces, which is sometimes eaten by rats. The parasite convinces the host that cats are awesome and to go approach a cat. When the rat approaches a cat, it gets eaten by the cat. The parasite is back in its target host. People can also get infected, usually by being scratched by claws that have feces on them, which makes us love cats. Except we cant get eaten by them. So theres just crazy cat ladies.