Toxoplasma gondii, a brain parasite spread by cat feces, can target and alter its host's feeling of fear!
Rats usually have an innate fear of cat urine. The fear extends to rodents that have never seen a feline and those generations removed from ever meeting a cat. After they get infected with the brain parasite Toxoplasma gondii, however, rats become attracted to cat pee, increasing the chance they'll become cat food.
This much researchers knew. But a new study shows the parasite, which also infects more half the world's human population, seems to target a rat's fear of cat urine with almost surgical precision, leaving other kinds of fear alone.
http://www.livescience.com/animalworld/070402_cat_urine.html - via Spluch