Just as your self is made up of numerous selves that are difficult to disentangle or even to distinguish absolutely, it's difficult to draw hard and fast lines between "your body" and "not your body". Are your vegetables part of your body? Is the farm that grew your vegetables part of your body? Is your yard (including the septic tank) part of your body? Do those circles widen? For example, is the water source that feeds the farm that feeds you part of your body? Where does that water come from? And is the creek that collects the runoff from your yard, then feeds the local river which ultimately runs to the sea part of your body?
Well, now this is part of your body. [Thanks to PZ Myers for posting the link on his blog, Pharyngula.]