Which of the following is NOT a common reason for aggression in dogs?

Playfulness is typically not considered a common reason for aggression in dogs. While dogs can exhibit behaviors that may appear aggressive during play, such as growling or roughhousing, these behaviors are more about social interaction than true aggression. Playfulness involves friendly behaviors that are intended for engagement and social bonding with other dogs or humans. In contrast, fear, territoriality, and frustration are recognized as significant triggers for aggression. Fearful dogs may lash out when they feel threatened, territorial dogs may defend their space aggressively, and dogs experiencing frustration—such as being restrained or unable to reach something they desire—can also exhibit aggressive responses as they try to cope with their situation. Understanding these different motivations behind aggression is critical for effective training and behavior management in dogs.