hope I'm doing this right – I did try a search first but couldn't find anything that seemed relevant.
Back when I was in middle/high school in the 90s, I would sometimes pick books off the SF/F shelves at the school library pretty much at random, just based on something about them that seemed interesting. One of them had a story that mostly wasn't very memorable, except for one detail that had stuck with me since: a character in the book (I think a woman? I'm sure it wasn't the protagonist anyway, but a secondary character, maybe even just someone he met) had created a world for herself which had all sorts of mythical creatures, including centaurs, but the only way she (?) managed to make the centaurs work properly was to give them a sort of breathing hole in the lower abdomen of the human part, that connected to the lungs of the horse part, otherwise they couldn't get enough oxygen and would die. That image stayed in my mind long after any other details about the book had faded away. I always thought it was a really interesting concept, and something that I didn't see in any other work.
For some reason I used to think this was a Zelazny book, possibly one of the Amber ones (like I said, I would just pick books that seemed interesting, so sometimes that meant I read a book from the middle of a series without reading the ones before it; this one was a book that I didn't like enough to try to read more of the series, if indeed it was part of one), but I'm not so sure now, since none of the people I talked to who had read the entire series found the description familiar, at all, nor did searches about it come up with anything.
Another detail that might be helpful is that this was in Israel, so there is a good chance that this is a book that had been translated into Hebrew (not a 100% chance, but most of the SF/F books in the school library were in Hebrew) at some point, probably more or less around the 80s. Unlikely that this was an original Hebrew work, since at the time there weren't many of those, and I think I would have remembered that; as it is, my vague memories of the book have a distinct "Anglo" (American?) feel to them.
Does this ring a bell for anyone? Is this a Zelazny, or something else? I'd really appreciate any help with this mystery.