Making Sense of the “12 Days of Christmas”

(via Today I Found Out) Even the most ardent fans of Christmas will agree – the song “The Twelve Days of Christmas” does not make a whole lot of sense. What is a partridge doing in a pear tree? Partridges are ground-nesting birds! So where did perhaps the most earworm inducing Christmas song in history come from, and why are there twelve days in it, instead of just one?