Behold the power of the Facebook newsfeed. A new study suggests that the emotional states in your friends' posts can actually be transferred to you. For the experiment, Facebook secretly played around with the newsfeed algorithm, forcing abnormally low numbers of positive posts or negative posts to show in over 600,000 users' feeds. Users who saw fewer positive stories then posted fewer positive posts and more negative ones. Just the opposite occurred when people saw fewer negative posts. The study indicates that “emotions expressed by others on Facebook influence our own emotions, constituting experimental evidence for massive-scale contagion via social networks.” On a different note, the study also indicates that Facebook is more than happy to unwittingly mess with you as an experimental subject.