Hmm. Never heard it before. It certainly sounds Carrollian (Why is a raven like a writing desk?), but I'm pretty well-read when it comes to old Charlie Dodgson, and it doesn't ring any bells.
Is it possibly a linguistics phrase demonstrating the opposite of the sentence "The gostak distims the doshes."? The "Gostak" sentence is an example of a sentence that parses perfectly well, but doesn't mean anything, while "Why a mouse" uses very simple vocab, but still has no meaning.
I thought there was a more canonical version of "understandable vocab, unintelligible parsing sentence", and there is: Noam Chomsky's "Colorless green ideas sleep furiously." So, I'm at a dead end, but perhaps I've sparked someone else's brain?
In order to add further value to this fairly fact-free post, I'll toss in this joke that I found in my googling for the above sentences:
Rebecca: What's green, hangs on the wall, and whistles?
Samuel: I don't know; what is green, hangs on the wall, and whistles?
Rebecca: A herring.
Samuel: But ... a herring isn't green!
Rebecca: Nu, so you could paint it green.
Samuel: But a herring doesn't hang on the wall!
Rebecca: Nu, so you could hang it on the wall.
Samuel: But a herring doesn't whistle!
Rebecca: Nu, so a herring doesn't whistle.
(Nu = Yiddish expression, sort of the verbal equivalent of a shrug)
