The crazy cat lady on your block might be more outgoing than you think.
Toxoplasma gondii, a common parasite that can infect humans who own a cat or eat a raw steak, can apparently cause people to be more extroverted and less conscientious. A study published in the European Journal of Personality concludes that "Toxoplasma manipulates the behavior of its animal host by increasing the concentration of dopamine and by changing levels of certain hormones."
While the parasite can be hosted by humans, it requires cats and rodent hosts to live out its full life cycle. Infected rodents lose their fear of cats, thus increasing their chances of being eaten—the parasite then uses the cat's body to reproduce and spread through its feces.
So if you're feeling a little socially anxious on a Friday night, skip the martini. Just go clean out the litter box and hit the town.