Dogs may lick their humans' feet as a sign of affection, bonding, and submission.
This behavior is rooted in their instinctual pack mentality.
The scent and taste of salt on human skin may attract them, while the action itself can be a form of grooming, akin to how they lick pack members.
Dogs also seek attention and may lick to communicate their desire for interaction.
Additionally, it could be a learned behavior reinforced by positive reactions from their owners.
Some dogs may simply enjoy the sensory experience of licking feet.
Overall, foot-licking in dogs is a multifaceted behavior with elements of social bonding, communication, and sensory gratification.
Additionally, dogs have a keen sense of taste, and the various scents on feet provide information about their owners' activities and well-being.