Our bodies may be (nearly) symmetrical on the outside, but our insides are a different story. Your heart, your stomach and spleen are all on the left side of your body, your liver on the right. But in one in 20,000 people, the sidedness of the organs is reversed.

Does organ symmetry have any effect on overall fitness – and how does your body know the difference? Joe Hanson explains, in an awesome new installment of It's Okay To Be Smart.