Why is a raven like a writing desk?

Carrollian conundrum posed by the Mad Hatter to Alice at the tea party:

The Hatter opened his eyes very wide on on hearing this; but all he said was, "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.

Alice sighed wearily. "I think you might do something better with the time," she said, "than wasting it in asking riddles that have no answers."

Lewis Carroll had this riddle riposted at him so many times that he wrote the following in his preface to the 1896 edition of his book:

Enquiries have been so often addressed to me, as to whether any answer to the Hatter's Riddle can be imagined, that I may as well put on record here what seems to me to be a fairly appropriate answer, viz: "Because it can produce a few notes, tho they are very flat; and it is nevar put with the wrong end in front!" This, however, is merely an afterthought; the Riddle, as originally invented, had no answer at all.

Alternative answers were ventured by various puzzle mavens, some of which were recorded in Martin Gardner's The Annotated Alice and More Annotated Alice: Sam Loyd, a turn of the century puzzle master, offered "Because Poe wrote on both", and "Because the notes for which they are noted are not noted for being musical." Aldous Huxley proffered, with his customary verve, "Because there is a B in both and an N in neither."

My favorite, unattributed: "Because they both have inky quills."