Turning science into poetry in the Old Testament, from the Song of Solomon seemed easy. "Thy lips, O spouse, drop the honeycomb, honey and milk under my tongue."
Today's writers are a little more challenged. In modern day, when we kiss, electrochemical currents rush from the brain along two main nerves that extend fibre to the facial muscles. The pupils dilate spontaneously when we are aroused. Enlarged pupils signal sexual interest to a potential lover. Anthropologists suggest that women may lick their lips as an unconscious way of reminding men of their lower lips, the labia, which enlarge to at least twice their original size with sexual arousal.
Why does kissing feel so good? Touch causes endorphins, along with a potent hormone called oxytocin, which surges at the though of connecting with a partner's lips. A kind or orgasmic chemical reaction occurs when we kiss; partly responsible for a delicious flood of desire, arousal, nipple response, erection and orgasm. The tongue is one of the most heat-sensitive areas, making our kisses hot. Through kissing, a flood of smell and taste sensations flow through our system. Think of how a kiss tastes, and why.
First kiss from Grace's Folly, a western historical romance:
"Wet skin dampened the delicate fabric of her blouse, allowing his body heat to penetrate with a searing intensity. Her arms looped around his neck. His hands tunnelled through her hair. Their lips met and clung. Nothing was tentative in their mutual desire to touch, to taste, to explore each other.
Grace had been kissed before, but nothing like this... this hot, hungry open-mouthed exploration where his need fueled her own and heady sensations spiraled out of control."
Saliva was considered by ancient alchemists to be a sexual elixir. Today, in a pinch, it acts as a very effective lubricant. As writers we have to use it all, past and present.