Did you know the nursery rhyme "Sing a Song of Sixpence" was originally used as a code to recruit pirates? Apparently it was used by Blackbeard and his allies. You can read the fascinating explanation here: http://www.snopes.com/lost/sixpence.asp
Yes it is. Ring Around the Rosy gives me the shivers now that I know it's about the plague! I have to sing it to my daughter sometimes, and conceal the shudders.