I am trying to find the origin / meaning of the phrase "oh musha, musha." I've searched the internet and various books on the origins of phrase and fable to no avail.

The two instances in which I have heard the phrase are: in the movie "Mary Poppins" - the fox says it while being chased by the hunters among whom Mary, Jane and Michael are riding horses from the merry-go-round. Secondly, it was in "The Quiet Man" - said by one of the spectators while Sean Thornton is practicing for the Innisfree cup.

Thanks in advance for any enlightenment you can provide!

It's from Irish Gaelic muise (pronounced /'mʌʃə/) 'indeed'. One etymology I've seen says it comes from mas ea 'if so'. In various places in a sentence, it can become mhuise (pronounced /'wʌʃə/ or /'wɪʃə/), spelled in Hiberno-English as wisha. It also seems to be a common euphemism for Muire (Mhuire) 'the Virgin Mary' (pronounced /'wɪrə/).