A much more credible version goes after this fashion:-

Sing a song of sixpence, a pocket full of Rye,
Four and twenty blackbirds baked in a pie,
When the pie was opened a shrivelled blackbird spat,
"Come on lads, a joke's a joke, what rotten sod did that?"

From the collected nursery rhymes of one Richard Digance, Troubadour.

Don T.