Sometimes we see a vid that makes us snort-laugh so hard, milk shoots out of our noses. Or one that utterly breaks our hearts. Or sets our inner outrage seething and bubbling over. We all know a viral video when we see one, but how many of us can really pinpoint that indefinable quality that grabs our attention and compels us to spread it around to others?

This video from PBS Off Book, which is no stranger to viral videos itself, seeks to answer those questions and more. Chronicling the early days of viral vids — remember "Where The Hell Is Matt?" — this mini documentary covers some of the world's most shared clips, all while raising a question of its own: Does the content we watch reveal something about who we are?

The Off Book series has been knocking it out of the park lately, with geek-approved topics like the the art of logo design, evolution of 8-bit art and a broad sweep on the culture of Reddit. For more, be sure to visit the PBS Off Book YouTube channel.