On the outside, people’s right and left sides look pretty much the same. On the inside, though, such superficial symmetry gives way to an imbalanced array of organs: The heart, spleen and stomach sit on the left side of the body, while the liver and pancreas take up the right. Even organs that at first glance appear as perfect mirror images of each other, such as the kidneys, lungs and testicles, turn out to have telltale left-right differences.
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