Why does my pet...?
Why does my dog sniff everything on walks?
Short answer: Your dog is reading. Scent marks on a lamp post carry information about who passed, and dogs are very good at following it: trained dogs could tell which way a trail went from about five footsteps.
Updated
In more detail
A dog's nose also sends part of each sniff to a separate smelling region.
The wild side
Wolves scent-mark along the routes and edges of their territory, and pay close attention to marks left by others.
Try this
Try a sniff walk now and then: a slower walk where your dog chooses where to stop and smell.
See it in the episode
Your Dog vs a Wolf: Who Has the Better Nose? (Wild Cousins, episode 4)
Questions people ask
Why does my dog sniff everything on walks?
Your dog is reading. Scent marks on a lamp post carry information about who passed, and dogs are very good at following it: trained dogs could tell which way a trail went from about five footsteps. A dog's nose also sends part of each sniff to a separate smelling region. If your dog suddenly loses interest in smells or sniffs in a new, odd way, ask your vet.
Sources
If your dog suddenly loses interest in smells or sniffs in a new, odd way, ask your vet.