Christopher Paolini has often been asked this in interviews.
His Word of God answer is usually No Comment.
Going back to when Eragon and Saphira coaxed the Menoa tree into giving them the Brightsteel – does the momentary pain in Eragon’s stomach have anything (or everything) to do with what the Menoa tree wanted from them?
Whatever the Menoa tree did or didn’t do, her plans are as long, intricate, and slow-moving as her consciousness.
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What did the Menoa Tree take from Eragon?
The Menoa tree did take something from Eragon, but I can’t say what without spoiling my next book set within Alagaësia.
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Please, please, please, share your knowledge... What did the Menoa Tree take from Eragon?! Or is that a "No comment" question?
No comment. :-)
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I think this might have been answered, but did the tree take something physical, magical, or metaphorical?
No comment.
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But he does say that we will eventually find out in the later books, specifically book V.
Will we ever find out affirmatively what the Elf tree took from Eragon?
Yes
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Before Inheritance came out, you always answered spoiler questions like "Go read Book Four" for such questions like "What did the Menoa Tree take?" It was never revealed what the tree took in that book. When you answer such questions with "Book Five" do you really mean that these questions will be answered in Book Five?
Yes. Those questions will be answered in Book V. (smart of you to ask!)
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Paolini also has confirmed that "Go" meant "leave Alagaesia"...
Fix me if i'm wrong-the Menoa Tree told Eragon to go..so she had probably meant that she wants him to leave Alagaesia, right?
That's exactly right.
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...but the tree did not take away or contribute to the prophecy of Eragon leaving Alagaesia.
Did the Menoa tree take the prophecy of leaving Alagaesia and never returning away from Eragon?
Good guess but no.
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Was the Menona Tree’s price for Eragon to leave forever?
No.
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Whatever it was that she took, it wasn't his or Saphira's ability to have children.
Can Eragon have children? Or did the Menoa tree take that?
Eragon can still have children (though given the changes from the Blood-Oath Celebration, might be difficult w/human or elf)
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Can Saphira still have children?
Of course. Dragon eggs for all.
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Did the Menona Tree’s price to take Saphira’s ability to have eggs?
No.
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Whatever was taken only affected Eragon, not Saphira.
Was Saphira affected by whatever the Menoa Tree took?
No.
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It also wasn't his moral regard for life.
I think I've figured out what the Menoa Tree took from Eragon. -a small part of his moral in regarding life (or maybe Eragon's regard for life is just disappearing slowly in general.)
Alas, no -- but it would certainly make for a great metaphor! You should be proud of your idea; it's one of the best I've heard so far.
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It wasn't death.
Did the Menoa Tree take death from Eragon (as in a incurable disease)?
No.
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It wasn't his or Saphira's Heart of Hearts.
There was an interesting theory that Eragon got a heart of hearts during the blood earth celebration and that the Menoa Tree took it. Can you confirm this isn't the case?
I can confirm that isn't the case. But that said, it's a COOL theory. Makes sense too: being given the heart of a dragon.
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Is it possible that the Menoa Tree took Saphira's Eldunari or does a dragon notices it if its Eldunari mysteriously disappears?
A dragon would DEFINITELY notice if their Eldunarí were snatched away.
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It wasn't even his appendix.
I vaguely remember that it was a twinge in his lower belly that happened when the Menoa Tree took something from him. Nowadays I'd have guessed it was his ability to have kids, but as a kid reading the book, I had just learned about how useless your appendix is, so I kind of assumed it was his appendix. Maybe useless to him, and food for it, or maybe has some other use that he'll have to compensate for later. Are either of those correct?
Ahaha. No comment. (It's not his appendix, though.)
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Paolini says the answer is possible to find out by reading the books, but he's so far only seen one person actually get it.
Has any fan guessed correctly what the Meona Tree took from Eragon? If not, is it just not possible to guess based on the books?
Someone may have correctly guessed what the Menoa Tree took (I haven't read every theory out there), but as of yet, I haven't seen a correct guess myself. Some readers have gotten really close to the truth, though. It's certainly possible to guess based off the books.
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Update here: I saw someone post a correct guess recently. Won't tell you where, won't tell you what the guess was, but someone finally got it. (Folks might have gotten it earlier, but this is the first time I've seen it written out correctly.) :D
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