I've heard from people who have worked with horses that horses don't realize how big they are. They observe the world from their heads, meanwhile their heads have no idea how big their bodies are.
Actually in New York, now until January 2009, there is an exhibit going on at the Museum of Natural History all about the horse. You see the posters all over the subway these days showing the Lipizzaner, the striking white horse that performs in civic functions, especially in Europe.
Related posts: My First Run-In with the NYPD and Code Yellow.