Mairzy Doats - Mares Eat Oats
“Mairzy Doats” is a novelty song from 1943 by Milton Drake, Al Hoffman, and Jerry Livingston.
From Wikipedia:
Milton Drake, one of the writers, said the song had been based on an English nursery rhyme. According to this story, Drake's four-year-old daughter came home singing, "Cowzy tweet and sowzy tweet and liddle sharksy doisters."(Cows eat wheat and sows eat wheat and little sharks eat oysters.)