Before you begin stalking a frenemy's tragic life on Facebook to feel a sense of schadenfreude, know this: that depression could rub off on you. At least that's the conclusion Facebook's researches came up with when they turned 689,000 users into guinea pigs for seven days, gaming what they could see on their News Feeds to see if it influences their moods. According to a paper recently published in PNAS, the social network used software to identify positive and negative words in status updates and to segregate posts into the two categories. Facebook then massaged the subjects' News Feeds to show mostly positive or negative posts. In the end, the company's researchers proved that emotions can be contagious even without direct contact on social networks, and even if you're only reading words on a screen.