Blend shaping a lion's face

One of the shots in the Serengeti project is a low angle shot of a lion striking a wildebeest.  To create the believability of the lion striking the wildebeest, I decided to put a blend shape in the lion's mouth to make it open and close.

How I did this was by selecting the model and going into the blend shape window; and creating a blend shape, which effectively created a copy of this lion.

I set a key at 0 in the Blend Shapes window, which meant that when the blend shape was set to 0, it would just appear as I modelled it.  I then moved the blend shape setting to 1, and with the copy of the lion, I moved the vertices so that it's mouth was open.  I set a key in the Blend Shapes window, meaning that when the blend shape set to 1, the original lion model would open its mouth as well.  I added the copy of the lion to a layer which I then made invisible.