This is just pushing and rubbing the face against the body of another living being. Infants do this once they start crawling (unless prevented, which is upsetting to contemplate) Adults can benefit from this as well, it is not just for other animals!
Rationale: Rubbing the face stimulates the ventral vagal system, (also known as the social engagement system). One can do this to oneself, but contact and feeling is increased if done with another 'energy system' (person).
Source: Traditional Bioenergetic Exercise