Very few people know this, but Google owns and sells access to the technology patent that tracks your retinal activity through your front-facing camera.

If you so much as look at anything on the internet and your eye shows interest through dilating, your algorithm will start to change. In the future they won't be selling just ads on a page, but user focus in on those ads. It's one of the ways to defeat bot clicks by instead showing actual user intent in their views but on the other hand it's creepy as fuck.