When you smile,you are creating a symbiotic relationship that allows both of you to release feel-good chemicals in your brain, activate reward centers, make you both more attractive, and increase the chances of you both living longer, healthier lives.
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I think the word 'soul' - it depends on what you define by 'soul.' If you're defining it as a mystical aura that is outside the body, I cannot measure that. If you're talking about soul as human nature, the rank of spectrum of behaviors and reactions that we know humans produce under certain circumstances, that is measurable.