Sing a Song 'o Six Pence: a pocket full of rye. Four and twenty blackbirds baked in a pie

Sing a song o' sixpence, a handful of rye,

Four-and-twenty blackbirds baked in a pie;

When the pie was opened the birds began to sing,

Wasn't that a dainty dish to set before the King?

So, what does this strange old nursery song mean? Or is it just nonsense? If you have never heard the legend of Gilligren and the King's pie you will scarcely understand the above verse; so let Frank Baum, the man who wrote the Wizard of OZ, tell you the whole story, and then you will be able to better appreciate...