The body of an animal is comparable with a machine like a locomotive. Actually it is a machine. It is made of many parts as perform some certain functions and fit for the roles with adapted specific structures, working synergically to complete a whole task. A locomotive needs fuel like coal, firewood or other combustible material to feed up. The body of an animal also requires fuel called food to provide energy to the animal. In order to burn the fuel in a locomotive and oxydize the food inside the body of an animal, oxygen is required. A locomotive is made of special structures: a hearth to take up and burn the fuel, pipes to transfer steam, wheels to move the machine and a chimney to expel the exaust. Similarly, the body of an animal is also made of various structures: an alimentary canal to take in and absorb food, an emunctory to expel the waste, vessels to transfer oxygen and store blood with nutrients, and legs or wings to carry the animal around.
