I don't support complete removal of individual books read or foods eaten as if it hadn't happened, but I'd be okay with these implementations:
hide from list - an option to hide certain foods/books from the 'read' list like an ignore list where they are maintained as still already fed/read but don't show up when you click through to view books read/foods fed lists. This allows the pet owner to curate their pet's memory list for a theme without removing the other site effects of the read/fed item (such as no longer being able to read that same book, for example, or counting in the number of different foods eaten).
complete clear/reset - I'd support an option to completely reset a pet to nothing remembered (remove all books read/int points spent/foods eaten/battles completed/stats trained/customizations/potions fed) basically turn it into a newly adopted pet of whatever species it is.
Why should you get to remove the food/book but keep the achievements? Also the main suggestion on here was to do so and get the item back (because you didn't mean to feed/read to X pet)....so then you've gotten the achievement and possibly the achievement prize and now you get to resell the item you used? Nah.
And even without that - if you're removing the item read/fed - why should you have an achievement for having done so?
Also, as I mentioned above....you don't need this function to get a pet with empty food/books. If you really really love the name of an adoptable pet....make one and swap names with it. There's a reason items are absorbed into the collections the way they are.
The only reason Stickers can be scraped away is because people can stick them to you without your permission. Nothing else needs to be removable.
This is also a nice compromise. Hiding them from public view works just as well!
Like I said, low ID pets are the reason we want removal or hide options. If you remove food or books from a pet, I should NOT be returned. No one in this thread is looking for that.
As for achievements... You don't lose already-earned food and book achievementz if you transfer or abandon the pet who has read them, do you?
What if my pet is a character supposed to be a normal mundane person? And it has read some weird anomalous book? That would not fly.
Even if we don't get a removal option, why not a hide option? What's wrong with more customization?
The OP was wanting the item(s) back. That's why they brought up how it could affect the economy.
You don't, but typically you put in the work to get there. This is wanting that work effectively erased but keeping the prizes for it. And it does affect achievements going forward - at least for totals on things read/eaten/etc. So if you can delete the cheapest books/foods and then refeed/reread them to your pets, you can obtain the tiered achievements faster. That's the point. The only way for that not to happen would be for staff to have that removed or to alter the way the achievement works so that it doesn't keep counting up after removal until a pet reaches that same number again. Some of these achievements take quite a long time and dedication to work towards.
Hiding them from view (in total or selectively) would be a more fair option to everyone. But also you can already do that with coding...staff doesn't need to make a toggle because you can change the profile and hide anything you don't want in view (like books read/foods eaten/stats/etc etc).
I'm not opposed to customisation and I think a "hide" option would be great for those who want it.
But I didn't just mention animals in my original post--people eat stuff all the time that they regret eating later. I take 2.5-5 mg of THC before bed to help with sleep and while it doesn't happen often, I have awakened the next day to realise I already ate that day's lunch when I got up at 3 AM and wanted a snack--and I have eaten food I was allergic to at work, parties, other people's houses by accident, because I didn't know what was in it and neither did they, apparently!
What I'm really trying to get at is that while everyone has the right to their feelings and I certainly understand OCDness, this is not really a big deal when you look at it in the context of how people and animals actually work. Most people who are vegan have not been vegan their entire lives. I was not gluten-free before I found out I had celiac disease. People accidentally eat things they're allergic to all the time.
As for weird anomalous books, IDK about you, but I have read tons of crap I wouldn't ordinarily read because I was stuck in a waiting room or an airport layover. This might sound weird in the current day due to smartphones, where you can get an interesting kindle book that you actually really want to read in seconds, but even nowadays, phones run out of charge and you can get stuck somewhere bored and willing to read anything that's remotely more interesting than the back of your hand.
I would probably never buy a book like "Funky Feet" but there have been situations when I'd have been more than willing to read it.
I'm not sure what the point of the reset option is for adopted pets that is suggesting, unless it's for situations where you really want a glade, steamworks or sweetheart pet, or a neela, but you can't afford to buy one, because if you have a pet slot, you can adopt a brand new pet that is a total clean slate. However, I am not opposed to it.

the pet reset is for people who care about the particular pet ID, whether it's a low number or just a special one to them, and the birth date of the pet. Which would not change on a reset.
I see. I was confused about why you would want to adopt a pet from the pound if you wanted a clean slate. :)

Maybe this particular thread got too messy for its own good. I might make my own, talking about the hide feature.
"" But also you can already do that with coding...staff doesn't need to make a toggle because you can change the profile and hide anything you don't want in view (like books read/foods eaten/stats/etc etc).""
You can't alter the code of a pet's read book and the like. It's impossible. We are talking about these pages: https://subeta.net/pet/books.php?petid=917281 https://subeta.net/pet/foods.php?petid=5916742 These ones cannot be edited. And a hide feature would suffice.
I guess I see what you mean but you used Qihanna as an example and her foods eaten list is 19 pages long, so...anything weird that's in there is going to get lost in all the rest of it.... Same with Derek and books!

Yeah, I know. I just used her as an example so you know what page I am talking about. Obviously I don't plan removing anythin from my main pet (who is the gourmand) either. But pets who I do not use for food. But one of my pets has a book that doesn't makes much sense for its character. And I wanna hide that.
you own SCP foundation? fangirls
EDIT: I guess what I'm getting at is that I've never once gone into someone's foods eaten or books read pages. I didn't even know they were public until I saw this thread.
I would probably not be too happy if everyone in the world could see everything I've ever eaten. But mostly because people who don't know I have a medical card and a chronic pain disorder and am actually NOT stoned all the time do not need to know how many edibles would be on that list. On the other hand, people would give up quicker on trying to convert me to vegan because my foods list would show that it clearly is a completely lost cause.

It's a work in progress. Check its treasure chest and you will see what I mean!
My other pets are all going to be Foundation researchers, and that's why I want their books and food to be "normal". Specially their books! I want them to resemble their field of expertise.
Well I can understand that (and I added to my earlier post above) but I also feel that if you're working with Clef and Kondraki you pretty much have the world's best excuse for having eaten and/or read something bizarropants.
EDIT: Now I'm thinking of if the whole world could see all of our food lists and realising that if they went all the way back to birth, a lot of human beings might have things like boogers, cat food, that paste everyone in kindergarten ate but me, etc in them--a friend of mine's baby brother was known for having eaten dead flies as a toddler--and people would be a whole lot more relaxed about their guilty pleasures lol.

I'm aware you can't alter those pages, but you can hide the viewability on the petpage if it doesn't fit with the theme you have (which was another complaint I read). Most people aren't running around using the web addresses to search everyone's pets so that was at least small workaround for not having it easily accessed/visible to others :/
Having a hide feature would probably be the ideal solution and would entail less coding changes to multiple areas of the site probably. A separate board might be a better option to suggest that, as I think it's going to get lost in this thread.