Licks are Pump’s way of making contact, her hand outstretched for me. She greets me home with licks at my face as I bend to pet her; I get waking licks on my hand as I nap in a chair; she licks my legs thoroughly clean of salt after a run; sitting beside me, she pins my hand with her front leg and pushes open my fist to lick the soft warm flesh of my palm. I adore her licks. I frequently hear dog owners verify their dogs’ love of them through the kisses delivered upon them when they return home. These “kisses” are licks: slobbery licks to the face; focused, exhaustive licking of the hand; solemn tongue-polishing of a limb. I confess that I treat Pump’s licks as a sign of affection. “Affection” and “love” are not just the recent constructs of a society that treats pets as little people, to be shod in shoes in bad weather, dressed up for Halloween, and indulged with spa days. Before there was any such thing as a doggy day care, Charles Darwin (who I feel confident never dressed up his pup as a witch or goblin) wrote of receiving lick-kisses from his dogs. He was certain of their meaning: dogs have, he wrote, a “striking way of exhibiting their affection, namely, by licking the hands or faces of their masters.” Was Darwin right? The kisses feel affectionate to me, but are they gestures of affection to the dog? First, the bad news: researchers of wild canids—wolves, coyotes, foxes, and other wild dogs—report that puppies lick the face and muzzle of their mother when she returns from a hunt to her den—in order to get her to regurgitate for them. Licking around the mouth seems to be the cue that stimulates her to vomit up some nicely partially digested meat. How disappointed Pump must be that not a single time have I regurgitated half-eaten rabbit flesh for her. Furthermore, our mouths taste great to dogs. Like wolves and humans, dogs have taste receptors for salty, sweet, bitter, sour, and even umami, the earthy, mushroomy-seaweedy flavor captured in the flavor-heightening monosodium glutamate. Their perception of sweetness is processed slightly differently than ours, in that salt enhances the experience of sweet tastes. The sweet receptors are particularly abundant in dogs, although some sweeteners—sucrose and fructose—activate the receptors more than others, such as glucose. This could be adaptive in an omnivore like the dog, for whom it pays to distinguish between ripe and non-ripe plants and fruit. Interestingly, even pure salt doesn’t kick-start the so-called salt receptors on the tongue and the roof of the mouth in dogs the way it does in humans. (There’s some disagreement whether dogs have salt-specific receptors at all.) But it didn’t take long reflecting on her behavior for me to realize that Pump’s licks to my face often correlated with my face having just overseen the ingestion of a good amount of food. Now the good news: as a result of this functional use of mouth licking—“kisses” to you and me—the behavior has become a ritualized greeting. In other words, it no longer serves only the function of asking for food; now it is used to say hello. Dogs and wolves muzzle-lick simply to welcome another dog back home, and to get an olfactory report of where the homecomer has been or what he has done. Mothers not only clean their pups by licking, they often give a few darting licks when reuniting after even a brief time apart. A younger or timid dog may lick the muzzle, or muzzle vicinity, of a bigger, threatening dog to appease him. Familiar dogs may exchange licks when meeting at their ends of their respective leashes on the street. It may serve as a way to confirm, through smell, that this dog storming toward them is who they think he is. Since these “greeting licks” are often accompanied by wagging tails, mouths opened playfully, and general excitement, it is not a stretch to say that the licks are a way to express happiness that you have returned.