Questions about Harry Potter and the Deathly Hallows: this is from a small Q&A Hermione did as part of a house-party of mixed Muggles and Magic.
Q: What was the weirdest detail left out of the book?
A: Fleur Delacour, having taken polyjuice potion and looking like Harry, snogging Bill with shocking passion while Moody went over the night's plan.
Q: Other details left out of the book / movies?
A: So many! Harry broke his leg as well as his arm and ribs crashing into the Tonks' pond. Ted Tonks was able to heal all of that along with his tooth. Hagrid, in the same incident, was left with a lifelong limp.
Q: How did it feel, being Harry for an hour under the influence of polyjuice potion?
A: Completely odd. The book records me as saying, "Your eyesight is really awful," which I did say, but not before some rather alarmed comments that would not have been suitable for a book read by anyone under the age of thirteen: that was a transfiguration that I found utterly shocking. (But my comments were nothing compared to Fleur's, who has always had a very French approach to the body, or Fred and George's. They were not above a very, very frank and unfair appraisal of Harry's body that I thought in utterly horrible taste.) In other words, I decline to answer the question properly.
Q: Were Beadle the Bard's tales in runes?
A: Yes, and the best workout in rune-reading I've ever had. Wizarding literature, language, and learning change much more slowly than for Muggles. Ancient runes were used well into the late medieval period, and learned wizards continued to study them for a few centuries afterwards. It really wasn't until the late 18th century that they died out of regular use and became a purely academic area of magical learning. In my opinion, that's a shame.
Q: How did your practical tactics evolve as you searched for the Horcruxes?
We got better at planning.
Q: Instead of wandering all over Great Britain, why not just make a base with a Fidelius Charm?
Because the incantation is highly advanced magic that none of us knew, and you can't always find such charms in books. Some spells are less like reciting words and more like walking a maze in your mind, and if you leave out a step, you'll get lost in the charm, and can actually do some pretty serious damage: imagine trying to perform the Fidelius Charm on our tent and finding out that we'd merely made it impossible to get in! Even if we'd known how to do it, we wouldn't have risked it.
To forestall the question: Flitwick or McGonnegal could easily have put a Fidelius Charm on Hogwarts before the battle, but you can't do it with that many people inside. The Charm relies on excluding all on the outside and including those on the inside. There were too many inside who, on leaving the grounds, would have been secret-keepers.
Q: Follow-up question: why did James and Lily have a secret-keeper at all besides themselves, and why Peter instead of Sirius?
We can only guess, since the only people who really knew are dead. But I think that it was James and Lily's intention to remain inside their house as long as they needed to in order to protect Harry. Lupin hinted that James was anxious to perform the charm to protect his family but put it off while waiting for Sirius. (Remember that the Order of the Phoenix at the time knew there was a spy among them, and James trusted Sirius as much as he trusted himself.) I suppose that they wanted someone on the outside who could bring them news and food. Probably the Charm was a little rushed, as Dumbledore had communicated the urgency of it to James, and it's almost certain that Sirius was not there when James was forced by haste to perform the charm. Pettigrew was likely on the spot (and in Voldemort's service, and probably there on his orders). He most likely offered his services, reminding James that time was wearing thin, and gladly took up the post of secret-keeper.
That's the most likely explanation.
Q: Could you explain a bit more about the role that The Deathly Hallows played in the Wizarding World before they were "found" by Dumbledore and Harry?
A: The Hallows were, as we discovered, somewhere between a religion and a conspiracy-theory. Wizards did not speak of the Hallows openly very much because they were so unattested except in legend and myth, and there was a whiff of craziness about them. Only eccentrics like Dumbledore and Xenophilius Lovegood acknowledged some sort of worth in the Hallows Quest, and even they would hardly ever speak of the Quest openly. That's why the lectures of Professor Binns told us absolutely nothing about the Hallows: he believed in facts. Or at least the facts that were acknowledged at the time of his death: I do not believe that to this day the old ghost has changed his opinion of the Hallows or admitted that they have played a role in the History of Magic.
But most Wizards had heard of the Hallows in more or less the same way that many Muggle children hear of the Holy Grail. A few could tell you what it was and what the legends actually were; but few indeed could tell you why the legends spoke so forcefully to people, or what the images stood for, or what one should do about it. Most of the Hallows believers I came across afterwards had treated the quest as itself significant, believing that through the quest for the objects, the soul would be purified to the point that one might eventually master death, if not physically, at least emotionally and spiritually.
Dumbledore and Harry, so far as I know, were the only ones to ever touch one (let alone two or three!) physical Hallows, so most seekers quietly despaired of the physical objects and resigned themselves to the hopeless quest in hopes of spiritual gains. In other words, they came to see the objects as real, but symbolic for the purposes of their Quest.
And they were not entirely wrong: Dumbledore acknowledged to Harry that possessing the Hallows was not enough, having discovered that the very desire for them can contaminate the Quest. The spiritual Quest was indeed more important than the physical objects themselves. Had Harry never possessed the Hallows, he still could have performed his sacrifice at the Battle of Hogwarts and saved us. Obviously, he was not the first or the last Wizard (or Muggle!) to so obtain the spiritual Hallows. In that spiritual sense, his own mother and father had done it, too.
But when he caught the Elder Wand that had flown from Voldemort's hand, he possessed the objects and the right to wield them. Questers went mad with delight (and envy). When it became generally known that Harry had defeated Voldemort through succeeding in the Hallows Quest, he took on the most messianic character in some segments of the Wizarding World, as if King Arthur or Jesus had returned. It is a burden he dislikes, but he knows better than to become either bitter or proud about it. He has declined many times to lecture groups of Hallows Seekers (some of whom naturally enough have therefore openly suspected him of fraud in the Quest).
Q: Did Rowling whitewash your relationship with Harry during the period that Ron was away?
A: No, not at all. By that time, Harry and I had long since determined we were not interested in one another romantically. The only awkwardness was that we were trying not to talk about Ron. I think Harry felt very guilty for provoking a division between me and Ron and didn't want to say so. Neither of us felt much like speaking our minds about it, and the Horcrux had a very bad impact on our mutual honesty.
Q: How did you ever get to be interested in Ron again after that? If a boy had walked out on me like that, I would not have become interested in him again.
A: You should consider several things before you judge him overly harshly. The most important was the effect that the locket-Horcrux had on him. Each Horcrux had a particular character that appealed to different weaknesses in people. Voldemort imbued the existing "traits" of already-magical objects with his own rapaciousness and malice.
Slytherin's locket (which already gave a charmed clarity to intimate, sensual desires and ambitions very forcefully) had a tremendous impact on Ron. We all noticed it. But that just happened to be Ron's weakness.
If I can tell tales on myself, I didn't fully understand how the Horcrux affected him until our thankfully-brief encounter with the diadem-Horcrux, which within moments exerted an enormous pull on me, much for the worse. It's quite likely I would have become just as bitter, angry, and disloyal had the diadem-Horcrux sat on my head for eight hours a day, tantalizing me with my intellectual superiority, my wisdom, and reminding me what fools surrounded me.
Remember that Ginny's passionate intimacy with the diary-Horcrux allowed it to prey on her in ways that the rest of us would not have fallen for quite so readily: its character and hers were a disastrous match, and I doubt that Harry would have succumbed to Riddle's influence through the diary unless he had used it for months and months.
So Ron was not entirely himself (or putting it more accurately, he was much too much himself) when he left us, a fact that was borne in on me in the days after his return. I am sure that's why it was so important for him to destroy the locket-Horcrux: it was necessary that he should overcome its power over him, which he most certainly did.
In the end, we never, ever, ever would have survived without Ron's constancy. He was relentless in holding us to our course after he returned, and Ms. Rowling's book could never convey enough how his steadfastness kept us on track. Quite simply, Voldemort would never have fallen without Ron, and I admired him enormously for it.
Q: The book has Harry and the film has you coming up with the idea to use the dragon to escape from Gringott's. Which is closer to the truth?
A: The book. But once I understood Harry's desperate inspiration, I was able to release the dragon and perform some simple concealment charms on us that helped keep us from its notice. They likely would not have worked on any sentient creature, but they helped us a bit in concealing us from the dragon. (I was disappointed to learn from my brother-in-law Charlie that I was not the first person to confund a dragon!)
Q: What did the House Elves really contribute to the battle of Hogwarts?
A: Their magic is fearsome when they're roused. They hospitalized a number of Death Eaters. Kreecher was quite mad, actually, and only barely restrained from killing several. I am quite sure Voldemort had only the vaguest understanding of how House Elves could threaten his plans: if they ever received the secrets of wand-lore, they would walk over the Wizarding World in a few days if they wished. But they are very cheerful and unfocused creatures, which is why they find so much happiness in receiving instructions and directions.