The Black Death

This is it, the king daddy of pandemics in human history, the absolute deadliest thing we've known to hit mankind - the Black Death.  Now, I know what you're thinking; why does the death have to be black?  Well, it doesn't especially; at the time, it was alternately referred to as the "blue sickness," the Pestilence, the Great Pestilence and the Great Mortality, although even those last two names seem pretty insensitive when you consider that it probably wasn't so great for the people living (and dying) through it.  About 800 years after its last major appearance in the Plague of Justinian (longer than it's been for us since the Black Death itself), the bacteria Yersinia pestis hitched another ride out of its origins in Asia inside the bellies of fleas riding on rats.  Fleas are jerks, but they didn't like the plague any more than humans did, since it was killing them too, building up in their guts and blocking the blood they drink from getting far in, starving the flea.  The flea tries to drink suck up some of that sweet, sweet vein juice from the rat, the dog, the human or whatever, but since their gut is all blocked up with plague bacteria, they puke up the blood, and some of that bacteria, back into whoever they're sucking on.  It probably didn't help when a Mongol army catapulted their own plague-ridden corpses over the walls into a Crimean city during a siege in 1347 either. Things were already pretty crappy across Asia and Europe at the time, too, since they'd just gone through the Great Famine (again, not that great) only 30 years earlier, devastating the climate (one of the reasons all those rats with their plague fleas were swarming human cities was that the fields had dried up) while crime skyrocketed as people did whatever it took to feed themselves (one popular theory about "Hansel and Gretel" is that the story originated from parents abandoning their children to fend for themselves during the Great Famine) and millions died.  It's important to note that people in the Middle Ages weren't necessarily any more the dull, dim-witted brutes of a Monty Python skit than we are today, but the 14th century, in particular, was a really shit time.  You see the things happening in the 21st century and how people think these are signs of the world coming to an end, but 14th century Europe was a much more religious society, somewhere from a third to a half of the entire human population was wiped out by a disease they had little to no scientific understanding of, all within just a few years.  Entire villages were obliterated, not to be discovered again until the advent of airplanes allowed us to see the world from above.  It only made sense to some people to march across the continent half-naked and whipping themselves on the back over and over until their bloody flesh was hanging off like stringy bits of barbacoa.  For some masochists, the plague may have simply been a convenient excuse, but officially, the idea was that mortification of the flesh was a symbol of their religious devotion and penance for their sins, believing that after enough penance, God would let off and end the plague.  Even the Pope and the Inquisition were like, "nah, cut that out guys."  Unfortunately, instead of ending the plague, it actually helped to spread it, as these "flagellants" (there is a joke to be had here about "flagellants and "flatulence") marched from plague-ridden town to plague-ridden town, whipping themselves silly and then taking the plague with them to their next stop.