The way we move, breathe, speak, or look can say a lot about what we are thinking or feeling. Understanding how to interpret the messages being sent through body language can help us make our characters more believable, and also prepare us for those author tours and speaking engagements writers get so nervous thinking about. Learning to project the image we want can make us appear more confident, and affect the way others perceive us.
There are individual and cultural differences to consider, but many aspects of body language seem universal. Understanding what it means can lead to more effective communication, and better writing.
Body Language explained:
http://changingminds.org/techniques/body/body_language.htm This site has about 70 pages of info on reading body language. Excellent source.
http://www.bodylanguage.netfirms.com/new_page_1.htm Quick overview of common body language meanings.