You clean my face i clean yours.

Dogs face cleaning exercise show display.
Play between dogs usually involves several behaviours that are often seen in aggressive encounters, for example, nipping, biting and growling. It is therefore important for the dogs to place these behaviours in the context of play, rather than aggression. Dogs signal their intent to play with a range of behaviours including a "play-bow", "face-pawed" "open-mouthed play face" and postures inviting the other dog to chase the initiator. Similar signals are given throughout the play bout to maintain the context of the potentially aggressive activities.
From a young age, dogs engage in play with one another. Dog play is made up primarily of mock fights. It is believed that this behavior, which is most common in puppies, is training for important behaviors later in life. Play between puppies is not necessarily a 50:50 symmetry of dominant and submissive roles between the individuals; dogs who engage in greater rates of dominant behaviours (e.g. chasing, forcing partners down) at later ages also initiate play at higher rates. This could imply that winning during play becomes more important as puppies mature.
Emotional contagion is linked to facial mimicry in humans and primates. Facial mimicry is an automatic response that occurs in less than 1 second in which one person involuntary mimics another person's facial expressions, forming empathy. It has also been found in dogs at play, and play sessions lasted longer when there were facial mimicry signals from one dog to another.
Dog-human
The motivation for a dog to play with another dog is distinct from that of a dog playing with a human. Dogs walked together with opportunities to play with one another, play with their owners with the same frequency as dogs being walked alone. Dogs in households with two or more dogs play more often with their owners than dogs in households with a single dog, indicating the motivation to play with other dogs does not substitute for the motivation to play with humans.
It is a common misconception that winning and losing games such as "tug-of-war" and "rough-and-tumble" can influence a dog's dominance relationship with humans. Rather, the way in which dogs play indicates their temperament and relationship with their owner. Dogs that play rough-and-tumble are more amenable and show lower separation anxiety than dogs which play other types of games, and dogs playing tug-of-war and "fetch" are more confident. Dogs which start the majority of games are less amenable and more likely to be aggressive.
Playing with humans can affect the cortisol levels of dogs. In one study, the cortisol responses of police dogs and border guard dogs was assessed after playing with their handlers. The cortisol concentrations of the police dogs increased, whereas the border guard dogs' hormone levels decreased. The researchers noted that during the play sessions, police officers were disciplining their dogs, whereas the border guards were truly playing with them, i.e. this included bonding and affectionate behaviours. They commented that several studies have shown that behaviours associated with control, authority or aggression increase cortisol, whereas play and affiliative behaviour decrease cortisol levels.
Empathy
In 2012, a study found that dogs oriented toward their owner or a stranger more often when the person was pretending to cry than when they were talking or humming. When the stranger pretended to cry, rather than approaching their usual source of comfort, their owner, dogs sniffed, nuzzled and licked the stranger instead. The dogs' pattern of response was behaviorally consistent with an expression of empathic concern.
A study found a third of dogs suffered from anxiety when separated from others.
Personalities
The term personality has been applied to human research, whereas the term temperament has been mostly used for animal research. However, both terms have been used interchangeably in the literature, or purely to distinguish humans from animals and avoid anthropomorphism​Personality can be defined by “a set of behaviours that are consistent over context and time”.[20] Human personality is often studied using models that look at broad dimensions of personality. For example, the Five Factor Model is one of the most commonly used models, and the most extensively studied. It is composed of five dimensions: openness, conscientiousness, extraversion, agreeableness, and neuroticism. Studies of dog personality have also tried to identify the presence of broad personality traits that are stable over time. Recently, dog’s personality dimension has been shown to be relatively consistent over time.
There are different approaches to assess dog personality: