Dogs have anal glands for releasing scents that identify them as unique individuals. These secretions include both foul-smelling scents and pheromones that have no scent at all. Dogs have a complex olfactory system that includes Jacobsen's organ in addition to their nose, for detecting odorless pheromones.A butt sniff in dogs serves the same function as a handshake in humans. A whiff of anal gland secretions tells as dog the other dog's age, sex, general health condition, and status in the dog's social order. Dogs wag their tails to release scents to welcome other dogs and move their tails to communicate changes in direction when they are running together.