Even if you aren't familiar with the term pareidolia, you've probably experienced some examples of it by now.
In my case, I couldn't help but notice as a kid that some of the cars that passed by while I was waiting for the bus looked a lot happier than others. The more rounded their headlights were, the more they seemed like they were smiling with their eyes.
And once you start to notice faces in a context like this, chances are good that you'll start to notice them in other places as well.
And as we're about to see, that doesn't quite scratch the surface of what else the things we commonly see can look like to us.