This Song first appears in a 1590 Prague Hagadah published by the family of Gershom Cohen . Had Gadya is generally thought to have been originally written in Judeo-German (the precursor to Yiddish). The first Aramaic Version we have reads "de-zabin aba" "that my father sold" rather than the later version "di-zevan aba" "that my father bought". It is thought that the original translator got mixed up in the difficult conjugations. The first Aramaic version also contains the line "ve-ata shunra ve-akhlah" "there came the cat (m.) and ate (f.). The feminine form could easily make sense in German even when the nickname Katzlein is neuter. (Guggenheimer) (Any dikduk geeks in the audience can confirm or deny this.)

While this song is a late addition to the liturgy based on a German folk-song, there are strong precedents in Jewish literature. From Bava Batra 10a : "Ten strong things were created in the world. A mountain is hard, but can be cut by metal, softened by fire, extinguished by water, clouds bear it, wind disperses them, body withstands it, fear breaks it, wine alleviates it, and sleep removes its influence. Death is the hardest of all." While I think the statement from the Gemara is a bit deeper, Had gadya is a bit more musical.