When you go online, there is a 100% chance that you will be part of an experiment. We are constantly observed, and tested upon, in the digital space, and more often than not it’s done without our knowledge or explicit consent. Many experiments are simple and narrow, focused on how to keep our eyeballs on a particular page, to how to get us to click a particular button, or how to separate people into categories where we can be subjected to particular exploitation - did your hotel or plane tickets cost more or less than another person on the same site? But should we be afraid of every test in the digital world? Aleks finds out how a glitch in the World of Warcraft resulted in the first virtual plague, and it allowed epidemiologists to study human behaviour in a pandemic situation, without risk of anyone really being harmed but in ways that were startlingly analogous to real world behaviour. And she delves into the now infamous Facebook Emotional Contagion study, and finds out that the public outrage may not only have been displaced, but could have done far more, and longer lasting, harm than could have been predicted.