Trophallaxis

Trophallaxis is the regurgitation of food by one animal for another. It is most highly developed in social insects such as the ants, in which individual colony members store food in their crops and regularly exchange it with other colony members and larvae to form a sort of "communal stomach" for the hive. It is also used by some vertebrates, such as birds feeding their young.

Trophallaxis is also perfomed by members of the dog family. In the wild, a hunting dog will regurgitate food gorged whilst far from its lair in order to feed its puppies. Ths puppies lick the face of the adult in order to trigger trophallaxis. Domestic dogs are tame because of arrested development of their wild tendencies and will treat certain humans, in particular their owner, as lifelong 'parents'. So when a dog licks your face, it's manifesting a vestigial feeding instinct. Most human dog owners, however, have not mastered the technique of performing trophallaxis when greeted by their pet, and nor do most dog owners lick the faces of their pets in order to obtain food (although in extreme circumstances this might be a useful survival tactic).

Trophallaxis serves as a means of communication, at least in bees.