I just started re-reading the series from the beginning, and there are tons and tons of errors. One thing that really struck me was this line in book one:
"four Andalites, standing all together, looking like a strange gathering of deer with solemn faces. Two of them looked very small--kids. I realized this was a picture of the Andalite's family." p. 20
I've read the first book a few times now, and that line never stuck out at me before because I just figured it was Ax + Elfangor and their parents, but for some reason, this time, I realized that was Elfangor's wife and kids. Elfangor's not a kid anymore--he wouldn't be one of the little ones. At this point, I think it's safe to say he's at least in his thirties, in human years. There's no indication anywhere in the series that Andalites remain "kids" that long, in fact, in the Gafinilan book, I think they remark that Elfangor was actually pretty big for an Andalite.
Of course, it's done in vague enough language that it's possible to argue either way, but I really think she fully intended for Elfangor to have an Andalite family before she retconned him being Tobias' dad. I've only read the first two and a half books, but I've come across a few more errors, let me see...
oh, in the second book, Visser Three picks up a cat carrier with a cat inside and choke-holds Chapman, when it's later indicated that Andalite arms are very weak (he can't even squish a Yeerk in his hand in book #29)
The nature of the Yeerk population--in book #1, V3 indicates that they'll need to breed more Yeerks to infest all the humans ("With this many hosts we can spread throughout the universe, unstoppable! Billions of us. We'll have to build a thousand new Yeerk Pools just to raise Yeerks for half this number of bodies." p. 36), while in later books, especially the Hork-Bajir Chronicles, it seems that within the Empire you have to be "selected" to infest a host, like there's more Yeerks than there will ever be hosts.
Oh then there's just stupid stuff, like that ridiculous book where the buffalo and ant got the power to morph, when it's clearly shown in the books that morphing requires a lot of concentration: "When you acquire, you have to think hard about the animal, focusing on it and blocking everything else out." (Book 2, p. 55)
w/e there are a ton of little inconsistencies. I really kind of like them, to be honest. I mean, if you think about it, Scholastic had about a month to write, proofread, and publish each of these books. Not only that, but like most TV shows, there's no end-point they're aiming for, it's impossible to make them entirely self-contained. I think KA even said at one point she had enough ideas to start off with for 12 books, and then it was like, "well, now what?" So mild contradictions for the sake of good storytelling don't really bother me, and not only that, but they leave ripe opportunity and inspiration for fanfic. Like what someone said about Andalite senses of humor--yes, in both the AC and Ax's flashback in #8, it shows that Andalites have a concept of humor, but maybe it's not based on the same thing as the human sense--I'd love to see a fic that explored that a little more deeply.
Anyway, obviously that's me being nerdy. For serious I'm going through the entire series and just taking notes of every inconsistency/clue/thing I find interesting. Cassie/Jake and Tobias/Rachel were already getting shipped in the first and second books. And there's a really interesting line on like the first page of book one that's something like "I'm good at video games b/c I get a lot of practice but Marco analyzes them for weak points and designs strategies, so he beats me sometimes." I think it's amazing that little stuff like that gets so wonderfully integrated into their characters later on.
Okay w/e I'll come back here when I notice more
