gif courtesy of http://fuckyeahnightmares.tumblr.com/

So I thought a fun/slightly creepy thing might be to find out what my fellow overeducated-in-a-good-way Groupthinkers think is the creepiest unsolved mystery from the past? To get the ball rolling, I will share mine: The English Sweat. It was an incredibly deadly disease that to this day remains a mystery. There are hypotheses, of course, but we honestly don't know what it was, where it came from, or if it will come back.

What past mysterious horror still gives you the horrors today?