Hello all 
Your first  "cut" is done on the main strap exposing a hole in the guitar strap.  Then you will need a bigger piece 1/4 inch bigger then the hole. about 3/5 oz leather . The shake skin is then glued on this part and glue on the back of the guitar strap, the sewing is done around it.  Then a full piece on the back of the guitar strap "chap leather" 2 OZ. 
You will never see the second part the 3/5 oz leather just the sewing on the front. 
that method is call inlay you can even put a piece of leather deer, mouse ect,,,(spongy) between the skin of the snake and the snake will look like it is standing up or "popping up" 
I did a few so far and the demand is very high, I learn that from a DVD I have best $120.00 spend on a movie 
PM me and I may be able to provide very good details.....