@ SM: This is not a good analogy because your left and right arms are seperate therefore they can resist each other.
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SM, your body doesn't know it's made of "parts". For convenience we humans staple labels on everything, including body parts, but as far as yor body is concerned, it is one harmonious, cohesive unit. It would be more accurate to describe your arms as an "aspect" of your body. Ditto for the brain.