"Why is a raven like a writing-desk?"...
"Have you guessed the riddle yet?" the Hatter said, turning to Alice again.
"No, I give it up," Alice replied. "What's the answer?"
"I haven't the slightest idea," said the Hatter.
-- Lewis Carroll, Alice's Adventure In Wonderland
And from Martin Gardner's The Annotated Alice: "Because the notes for which they are noted are not noted for being musical notes."