Mattresses are friendly, dim-witted, docile creatures capable of speech. They are all called Zem and live in the swamps of Sqornshellous Zeta. Many of them are slaughtered, dried out, and shipped around the galaxy to be slept on by grateful customers, though they do not appear to mind this, one noting that since they are all called Zem they never know which of them have been killed anyway so their concern and grief - "globbering" - is kept to a minimum. The book Sqornshellous Swamptalk is a dictionary of mattress vocabulary.