They zip around the house at breakneck speeds playing tag. They get into the cupboards and rattle the dishes (even if you get up and catch them doing it they'll sit there and deny that it was them). They howl and "talk" (just to hear their own "awesome" voice). They jump in and out of the window using my head as a launching/landing pad (they claim they're on guard duty). They have hairballs. Not friendly "hack, hack", hairballs, but puked hairballs. And they have to do it loud enough so as to be heard in the next state! Then they'll get really quiet. So you lie there in bed wondering ... where is that hairball? It sounded close, but cats are great ventriloquists. Is it someplace where I'm going to step in it in the dark or is it on the kitchen table? Worse, will they step in it and track it across my face if I fall asleep? Then just as you finally drift back to sleep the alarm goes off. You reach to shut it off only to find the hairball.
Almost nothing, I sleep the sleep of the just and the true. Seriously, I have a clear conscience and a strong personal moral code that allows me to sleep soundly at night