however, sadly the thing is behaving as though the button on its forehead is stuck, so it can't actually shut off and stay off. so now the batteries are removed while I decide what to do with it.
there's at least one report of zinc whiskers forming causing the same symptoms https://www.reddit.com/r/furby/comments/1hn3vk8/fixed_2023_purple_furby_heart_button_not_working/
also I've found documentation of multiple teardown attempts that quickly descended into "fuck it, I'm not putting this thing back together again", which doesn't inspire confidence