from "What Do Dogs Know?":
and humans obviously differ in many ways. One of
the most important differences is in how the two
species perceive the world. For instance, dogs have
an incredible ability to read scents. If you could
unfold the inner surface of a dog's nose (the part
with the cells that allow the dog to smell), it
would actually cover a surface area larger than
the entire extent of the dog's skin.
Dogs read the state of the
world through their noses, and they write their
messages to other dogs in urine. A particular dog's
urine contains a lot of information about that dog.
It smells different depending upon the dog's age
and health; whether it is male or female, or a female
in heat; and even depending upon the dog's emotional
state. For a dog, sniffing a fire hydrant or a tree
along a route popular with other dogs is a means
of keeping abreast of current events.That tree is
really a large newspaper containing the latest news
items in the dog world, and perhaps even installments
of classic canine literature.