Answers: Why is a raven like a writing desk...?

Some facts:

• Lewis Carroll (né Charles Lutwidge Dodgson) includes this riddle in the Mad Hatter's dialogue with Alice in her Adventures in Wonderland [full text here].
• The riddle is not answered in the text. Some time later, due to the unanswered riddle's popularity, Carroll provided his own answer; which—interestingly—included an inversion pun that was accidentally "corrected" by an editor who didn't get it.
• People have been puzzling (riddling...?) over the riddle ever since, or making up their own answers.
• When I went to find a compendium of answers on the Internet, the results were mixed—nothing comprehensive.

Here's the riddle in context:

From Chapter VII. A Mad Tea-Party

‘Your hair wants cutting,’ said the Hatter. He had been looking at Alice for some time with great curiosity, and this was his first speech.
‘You should learn not to make personal remarks,’ Alice said with some severity; ‘it’s very rude.’
The Hatter opened his eyes very wide on hearing this; but all he said was, ‘Why is a raven like a writing-desk?’
‘Come, we shall have some fun now!’ thought Alice. ‘I’m glad they’ve begun asking riddles.—I believe I can guess that...' 

The section between asked and not-answered is rather long—a twisty~turny exposition of some 550 words, most of them spent upbraiding Alice for her presumptuousness and so-called sanity.

Here was Carroll's eventual reply, provided in his preface to the 1896 edition of Alice's...:

"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 be a fairly appropriate answer, viz: 'Because it can produce few notes, tho [sic] 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."

That "nevar" is of course the purposeful mistake: raven with "the wrong end in front."

And following, then, is every one I can possibly find, as best sourced as I can manage. Please, please do correct me on any details; though I'll only make a change if you can back up your revision with some reference. And finally, I'm including my friends' takes here. It seems only fair. So please, please do submit your own:

Why is a raven like a writing desk?

(Best to presume a "Because" on each, just because...)

• It slopes with a flap.
   — Arthur Cyril Pearson, The Twentieth Century Standard Puzzle Book (v2), 1907
• The notes for which they are noted are not noted for being musical notes.
   — Sam Lloyd, Cyclopedia of Puzzels, 1914
• Poe wrote on both.
   — Sam Lloyd, Cyclopedia of Puzzels, 1914
• Bills and tales are among their characteristics.
   — Sam Lloyd, Cyclopedia of Puzzels, 1914
• They both stand on their legs, conceal their steels/steals, and ought to be made to shut up.
   — Sam Lloyd, Cyclopedia of Puzzels, 1914
• There is a B in both, and because there is an N in neither.
   — Aldous Huxley, “Ravens and Writing Desks," Vanity Fair, 1928
• It bodes ill for owed bills.
   — Francis Huxley, The Raven and the Writing Desk, 1976
• They each contain a river—Neva and Esk.
   — Francis Huxley, The Raven and the Writing Desk, 1976
• Both have quills dipped in ink.
   — Martin Gardner, More Annotated Alice, 1990
• Without them both Brave New World could not have been written.
   — Roy Davenport, The Spectator competition, 1991
• They are both used to carri - on de - composition.
   — Noel Petty, The Spectator competition, 1991
• One is good for writing books and the other better for biting rooks.
   — George Simmers, The Spectator competition, 1991
• One has flapping fits and the other fitting flaps.
   — Peter Veale, The Spectator competition, 1991
• A writing desk is a rest for pens and a raven is a pest for wrens.
   — Tony Weston, The Spectator competition, 1991
• With some skill it will emerge from the wood.
   — Q, A Drink With Clarence Mangan [blog], 2012
• It supported that noble effort, To Kill A Mockingbird.
   — Q, A Drink With Clarence Mangan [blog], 2012
• Neither is ever approached without caws.
   — Esther Inglis-Arkell, writing for io9, 2012
• Both are covered in inky quills.
   — Andrew Elliott, 2017
• They create unkindness when gathered to no good purpose.
   — Jeff Wills, 2017

Undated:

• "Raven" contains five letters, which you might equally well expect to find in a writing desk.
   — Roger Baresel
• A raven makes no sense, and so does a writing desk.
   — Linus Connell
• Neither requires the other.
   — Linus Connell
• It can be found in a class with a Writing Master.
   — Fernando J. Soto
• Both have a flap in oak.
   — J. Tebbutt

Unsourced and/or anonymous:

• Neither one is made of cheese / aluminum / etc.
• The raven wanted to be.
• They both stand on legs.
• You can baffle the billions with both.
• You cannot ride either one of them like a bicycle.

 

Sources; most (or many) in one way or another by way of The Annotated Alice or its sequel, both by Martin Gardner:

A Reader's Miscellany: https://nargaque.com/2010/05/28/why-is-a-raven-like-a-writing-desk/
A Drink With Clarence Mangan - Solutions to a famous raven riddle: https://manganpaper.wordpress.com/2012/09/23/solutions-to-a-famous-raven-riddle/
The Guardian: https://www.theguardian.com/notesandqueries/query/0,5753,-2083,00.html
StackExchange - Literature: https://literature.stackexchange.com/questions/702/why-is-a-raven-like-a-writing-desk
Reddit - Riddles: https://www.reddit.com/r/riddles/comments/3bvoif/alice_and_wonderland_how_is_a_raven_like_a/#bottom-comments