Clumps of dust exist under every piece of furniture, especially those you think you vacuum under and those wedged into the carpet.
There are scuff marks, rub marks and "goodness what the hell that is" marks everywhere, including the roof!
And if you have children (or a man child) there is food in places you didn't know existed, and I'm not talking about a few crumbs, I'm talking about a village of half eaten apple cores, popcorn kernels and biscuits that have gone on dates, married and are now breeding!
Be prepared!