The cat-loving parasite with a creepy reputation for hijacking its host's behavior is using the infected body's own immune system for transportation, but also to juice it with a neurotransmitter that can suppress fear. There's a growing body of research about the extent to which Toxoplasma gondii can affect the behavior of its host, and a recent study shows the single-celled organism has a sinister ability to hijack the very immune system cells meant to defend against it. It also causes the cells to secrete a neurotransmitter that makes the cells travel faster, but is also associated with reduced fear and anxiety.

Toxoplasma is known for reproducing in cat digestive systems, spreading to the bodies of living rats through cat feces, then steering the rats toward other predators to complete the life cycle. When the protozoa travels from cat poop to rodents, it can enter the brains of its hosts and affect behavior. Primarily, it makes the rat fearless or attracted to the smell of cat urine. Since the organism can only reproduce in another cat, this is Toxoplasma's clever way of getting back to its breeding ground.