Foxes, like felines, are mysterious. They can be quite stealthy and quick, and they have a measure of grace about them that would seem impossible. They are elegant and balanced at all times.
In addition, there is the appearance, and the trademark sumptuousness of the fur. The lines of the body are smooth and curvaceous. The colors are pure and rich, never bland. The face is marked with wit and cunning.
http://estes.on-line.com/wildwatch/Images/Fox.JPG
But most of all, you will probably only hear men describe a woman as a "fox" when they don’t know her very well or at all—in particular, never hearing her voice, I think. It is that mystery, in addition to the physical appearance, that draws the man in. She must remain mysterious to remain a fox.
-Tim