i have not put very much time into the animals (tiger and snake are the only ones i still practice) i prefer the 5 fists and the linking form for my personal hsing i practice.
maybe in a broad sense the animals do the same thing. for example the snake http://www.youtube.com/watch?v=EUSEV...5&feature=plcp
it transfers mass in a different direction than any of the five fists.
the dragon goes more up and down etc. one of the things i look for in forms or martial arts movements is what makes it different what angle is it attacking or defending? what direction is my mass going?