Recently, there have been news stories about scientists who are cloning pigs. Well, maybe not so bizarre. Medical science has been using animal products to treat human disease for years.
Diabetics take insulin derived from pigs.
Some vaccines are derived from animal diseases. Pigskin has been used for grafts on human skin. When they view the body as a physical machine divorced from any soul or spirit, it is easy. A body is a body. Parts are parts.