More examples of visual metaphors here @ Pinterest: http://www.pinterest.com/xxxanafonsoxxx/visual-metaphors/
.... Wich brings to mind this old 2007 post about the importance of brainstorming your concepts before making that illustration and how it's perfect when you manage to grasp the idea and have the draftsmanship to nail it down.
[my drawing according to an article on: HELLER, Steven; ARISMAN, Marshall -The Education of an Illustrator. New York: Ed. Allworth Press, 2000.]