Never heard the one about the origin of the TDoC.

"Ring Around the Rosie": this one is supposed to re-create the pandemics that hit Europe in the middle Ages.

Ring Aroudn the Rosie: Both bubonic plague and small pox produce rashes at different stages of their progression; in particular, bubonic plague can produce a very bright red ring of pustules.

Pocket full of posies: There was a time that it was widely believed that pleasant smells confer some immunity to highly contagious diseases; flowers were often carried on one's person to ward off the current disease.

Ashes, ashes: With people dropping left and right, it often became necessary to cremate the masses of dead. Also, it was often that large outbreaks of fires would follow a local epidemic, since there were far fewer people to prevent small fires from becomming large ones.

We all fall down: Yeah, dead.

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