Ads are ubiquitous on the internet, and even if you use an ad blocker or two, you're bound to see a few things slip through. Luckily, those ads don't really give advertisers any new information about you unless you interact with them... right? Not so fast. Eye tracking technology can glean an enormous amount about your attention, as well as your reactions to a given image or piece of language, just by watching how you watch, gaze or glance at an ad. So how much can they learn, exactly? Does eye tracking allow companies to, in some sense, read your thoughts?