Why do dogs sniff each other?

Dear Yahoo!:
Why do dogs sniff each other?
Tarna
Dear Tarna:
Last year, we addressed why dogs love to stick their heads out car windows. Now we tackle another of life's great mysteries. What's up with a pup's propensity to sniff the backsides of his friends? Such behavior would not go over well in the human world, but in the canine community, it's standard operating procedure.
A dog's nose is its strongest weapon. In fact, it works up to a million times better than a human's. A dog uses its nose not only to sniff out dead birds in the backyard and burgers on the BBQ, but also to better understand other dogs. According to Point Ask, a sniff of the rear tells a dog all sorts of things, including what the other dog likes to eat, its general health, and if a female pooch is pregnant.

Dogs also use their olefactory talents to understand humans. This article by Meg Moss explains that, with one whiff, "a dog can tell where you have been and what you have been doing, what you have eaten, and even whether you are not feeling well." Moss goes on to say that when dogs sniff each other, they learn whether or not the dog is safe to play with or if they should retreat. Basically, it's just a way of getting to know each other. Although it's apparently an effective means of introduction, we're sticking with the handshake.