It's woman's intuition plus the fact that she's lived with you for more than ten years, and also observed you psychological and personality formations. Not mind reading, but almost as good.
Personally I hold that "woman's intuition" is a total crock -- if anything it's just that women are socialized to be a little more open to seeing emotion in other people, and analyzing what it means.
Looking over some homework that my English teacher emailed the whole class. I feel like coming into class whenever the hell we have school again and telling her I didn't have power, therefore I couldn't do it. *sigh*.