"Rigor Mortis" -What is and how does it work?

This is my first experience in looking up a question that was answered in Yahoo . Hope that this question wasn’t answered 100 times already, but I can’t seem to find a better definition than what I read in one response by the gentleman in the UK. I was watching a flick whereby rigor mortis was a subject of discussion and thought I would see about getting more details from the internet. That's when I came upon your answer to the definition of what it is and thought I could ask if you might know a little more about it. I'm curious if it's true that it starts in the brain after death and continues throughout the muscles. By the description that I heard in the movie (which isn’t always accurate) I was curious how after death the brain could produce a chemical which travels throughout the body affecting muscles. I was also curious if this takes affect in the entire mammals spiecies.