[Koha] Searches with "Not" in the title

Hi all, I'm trying to explain to one of my librarians why searching for a book titled "Not Hungry" (without the quotes) will bring up no results, while searching for "hungry" (without the quotes) will bring up the book. I'm guessing it's because "Not" is an operator...but I can't seem to find where this is explained in the Koha docs ?? (search operators that is...)