Dogs lick each other's mouths for several key reasons related to their social behavior and communication. It is a form of social bonding, affection, and respect among dogs. This licking often signifies that dogs are comfortable with one another and ready to play, or it can express deference from a lower- ranking dog to a higher-ranking one to maintain harmony in their social group. Puppies lick their mother's mouth to encourage regurgitation of food, and this behavior can carry into adulthood as a display of affection or submission. Additionally, licking can trigger pleasurable endorphins in dogs, strengthening social bonds and making the dogs feel good both when licking and being licked. Excessive licking, however, can signal anxiety or behavioral issues.