"Mairzy Doats" is a novelty song composed in 1943 by Milton Drake, Al Hoffman and Jerry Livingston. It was first played on radio station WOR, New York, by Al Trace and his Silly Symphonists. The song made the pop charts several times, with a version by the Merry Macs reaching No. 1 in March 1944.
At first glance the song's refrain, as written on the sheet music, seems meaningless:
Mairzy doats and dozy doats and liddle lamzy divey
A kiddley divey too, wooden shoe?
However, the lyrics of the bridge provide a clue:
If the words sound queer and funny to your ear, a little bit jumbled and jivey,
Sing "Mares eat oats and does eat oats and little lambs eat ivy."
With this aid, the refrain is quite easily comprehended, and the ear will detect the hidden message of the final line: "A kid'll eat ivy too, wouldn't you?"
http://library.umkc.edu/spec-col/ww2/warnews/rams/c/mairzydoats.ram