First week with a kitten: what nobody warned you about

The guides cover vaccinations, food and safety. They tend to skip the small shocks: how loud a kitten can be at 3am, how fast they find the one gap behind the washing machine, and how quickly a calm adult cat can become deeply offended. If you have brought a kitten home recently, what caught you off guard? And what would you tell someone collecting theirs this weekend? Background reading: kitten first 90 days and introduce two cats