Yes its the bodys' way of ridding it of waste products like undigested food, toxins and mucus
It is natural and required as the body has to have a way of removing waste from its system
An element is a substance in its pure and natural form.
Its a natural and essential part of animal existence
a natural substance is something that is found again and again in many different forms eg. salt (also a reoccurring substance)
sunlight
Yes it a natural way of removing waste matter from the body
Bunnies don't really eat their feces, but they do eat their cecotropes, and this a natural and healthy process. See the related questions below for more details.
Natural gas, gasoline, and kerosene are some fuels made from petroleum.
Yes.
Natural gas is a physical substance.
Natural Resource
Yes, stone is a natural substance, not man-made.