I am trying to create an expanding pool of blood. I found this great tutorial:
http://ae.tutsplus.com/tutorials/vfx/quicktips-how-to-create-a-realist ic-pool-of-blood/
However, this method only works with a plain ol' pool. I am doing a project where I need the blood to run down in a thin stream and then it expands into the pool (so it would look more like this: http://bearingdrift.com/wp-content/uploads/Blood_009_by_stock_ings_cut 1.jpg)
This doesn't work using the quick and easy method in this tutorial with the mask expansion. 
The reason I need to do this is because I am making a video projection of this blood that will be interacting with a large 3D sculpture (not in the video).
The guy who made the above tutorial told me I need to animate the keyframes instead - but for the life of me, I can't find any tutorials on how to do this.
I am using CS4, and I am a noob in after effects. Can anyone suggest a tutorial? Or, can I just make it so the expand isn't coming and going in the dead center, cause if I can change the position, I think that would work.
Thanks!