It is hardly a secret that Facebook manipulates users’ news feeds for advertising purposes, but according to Venture Beat, the social media company recently went one step further, experimenting with positive and negative Facebook posts to see how they impacted the moods of users.

The experiment was simple: Flood a user’s news feed with positive or negative content, and see how that person responds to the impulses. Based on Facebook’s findings – which were actually published in the form of a paper in the Proceedings of the National Academy of Sciences scientific journal – these “emotional contagions” actually did have a notable impact on the emotional moods of users.

The results of the experiment are about what you would expect them to be: When Facebook injected negative content into a news feed, users receiving those impulses became more likely to make negative posts of their own (or at least to make fewer positive posts). When positive content was flooded into a feed, meanwhile, the opposite pattern occurred. In other words, Facebook feasibly has the ability to manipulate the emotions of its users, just by toying around with what appears in the news feed.

Naturally, a study based on manipulation is destined to draw some ire from Facebook users, who have already fought back against the social network’s tendency to play around with the boundaries of online privacy. Facebook says that all users agreed to participate in any experiments when they agreed to Facebook’s terms of services.

Still, while Facebook is legally at will to do pretty much whatever it wants – and while only 700,000 of Facebook’s billion-plus users were studied as part of the experiment – it is incredibly doubtful that many or any users will be okay with being Facebook’s lab rats. And since Facebook earns the vast majority of its revenues from advertising, the company should be careful in alienating its treasured user base.