A new book by Sheril Kirshenbaum explores what our lips are telling us, and how we can listen to the animals of our bodies. “Because a kiss brings two individuals together in an exchange of sensory information by way of taste, smell, touch, and possibly even silent chemical messengers called pheromones (odorless airborne signals), it has the potential to provide all kinds of insight into another person. So even when our conscious minds may not recognize it, the act can reveal clues about a partner’s level of commitment and possibly his or her genetic suitability for producing children.” This quote, from Kirshenbaum’s book The Science of Kissing: What Our Lips Are Telling Us, offers a glimpse into the in-depth research behind the act of lip-locking; from the neurochemistry and evolutionary biology, to the social science of how it is humans came to kiss one another as greeting, sign of affection, or to denote sexual desire.

It’s a thought many of us have had before, am I right? As much as I love making out (and I love making out more than the average person, according to statistic-based research I’ve conducted on the romantic or sexual interests I’ve developed in my lifetime thus far), there have definitely been moments where I’ve been acutely aware that another person’s tongue is snailing along my tongue, their lips—through which they breathe, yell, consume, hold cigarettes, open plastic packaging, press against heads and pieces of paper and books—are one my lips, which have done similar things. Sometimes, I imagine all of the world pressing together in that moment as divine collision, a lesson in calamity physics, that combines object with sensation with a redefinition of crashing with, yes, germs. After all, didn’t you too grow up with the fear of mono struck deep into your heart?

That’s all to say: kissing. It’s a little weird, you know?

According to the research done by Kirshenbaum, kissing isn’t as weird as we may think. In a short film based on the book, It’s Ok To Be Smart shows visually what happens with the body when two (or more!) people come together to make out. A kiss begins with the eyes, that lock on the lips—the lips, say science, being unique to humans as animals. Lips, which 8 out of 10 women paint some shade of red, which calls to mind our primitive ape ancestors, who were attracted to the rosiness of.. well, baboon buns. The lips, state the video, initiate the physical response to visual sexual stimuli, as well as demonstrate (on a neurochemical level) fertility.

That’s not so difficult to understand, really. We are animals with animal drives, including the conscious & unconscious reactions to the possibility of procreation, but what is particularly interesting about this research is the proposition that kissing come from breastfeeding, or suckling—essentially breastfeeding as a child’s first exposure to kissing in the world. Breastfeeding chemically releases oxytocin, sending waves of pleasure throughout the body. Due to the free association of the action of puckering ones lips to receive pleasure, it is speculated that humans feel similar feelings of exhilaration during heavy make out sessions.

You know. If you thought kissing was weird before, there you have it.

Kirshenbaum addresses the general disparate lack of information about kissing and its origins by speculating on a few possible key reasons: “Scientists are not exactly sure why we kiss. This may be in part because they have not even definitively decided what a kiss is. Unlike most other areas of scientific investigation, there’s no accepted “taxonomy,” or classification system, for different kinds of kisses and closely related behaviors. What’s more, you don’t find the experts crunching the numbers and figures on kissing across world cultures, as researchers would surely do if they wanted to get a handle on the available data. Why so little analysis of osculation? Perhaps kissing seems so commonplace that few of us have paused to reflect on its deeper significance. Or it’s possible the subject has been intentionally avoided under the microscope given the challenges of interpreting what a kiss really means.”