This is the final piece– the  platypus in bronze.

The piece begins with forming the platypus out of clay, as seen in the first four photographs below. Next a mold is made from the clay model (pictured). That mold is used to make a wax replica (also pictured), around which another mold is made. The wax is melted out of that mold and bronze poured in. This mold is destroyed when the bronze platypus is removed. The metal is then checked for imperfections, a patina applied, and the piece is done.