Pixies. They come out at night when we're all asleep -- well, most of us -- and they tidy the place up a bit**, stick a new hamster in the wheel and away it goes.
** they have a request for Teebs, by the way; if you're going to leave those things hanging around, could you at least put them in a bin bag. One of the pixies is having great difficulty getting the stains out of his tunic.
Yup, it's been a lot nicer.