According to Smithsonian philematologists (scientists who study kissing), when we Kiss, we exchange 9 milliliters of water, 0.7 milligrams of protein, 0.71 mg of fats... and somewhere between 10 million to 1 billion bacteria. So why do it? Why expose yourself to the risks of orifice-to-orifice contact, which include disease, infection, beard burn, and tasting someone's bad breath?

Well... Science is still working on that one. One of the confounding things is that kissing is not a universal human trait - it's a relatively novel practice, evolutionarily speaking, and there are plenty of cultures that do not engage in romantic or sexual kissing. This suggests that it is more of a learned behavior than anything hardwired into our circuitry. The most likely explanation seems to be that kissing is a strategy for testing a potential mate's genetic code.

Women particularly favor kissing, and especially during the early stages of a relationship, with the thought being that if a partner tastes bad to you it's less about what they had for lunch and more about searching for signs of disease, genetic imperfections, and detecting little guys called major histocompatibility complex genes.

Humans are capable of tasting and even smelling MHC genes, which can indicate just the right amount of biodiversity in order to optimize your chances at having a healthy baby. So maybe Betty Everett was more right than she knew when she told your grandma "it's in his kiss."