Not quite sure what you are asking by center balls?
This is a regular butterfly shot, with an extra ball in each of the 4 corners. From the cueball, there are 2 additional balls frozen, that go into the side.
The way the butterfly shot works, is the 4 "end" balls are all combination shots, aimed to allow for throw into the corner pockets. The "center" balls are dead caroms off of the back 2 balls into the side pockets.
To me the hardest part of shooting the shot that she did is to make sure that all 8 balls go into the corners. It takes a loose table with the hanging balls very deep, and off to one side of the pocket.
Hope this helps?
Chuck
