Via dal veterinary go to the vet
Probably not a breed thing or exclusive to pugs. Often food or seasonal allergies will cause dogs to itch and pugs are often overweight which exacerbates their regular physique (barrel chest and short legs) and can ' t bend to scratch the center of their chest easily so scraping it across the floor feels good.
My mom has a pug, and I had a pug a few years ago, I'm not sure, it seems to be just a trait, certain breeds of dogs will inherit different random traits. All the pugs I have known have also showed these traits:
1. They like to "back-talk" and yap when they are young
2. They tuck their butt and tail under them when they start running around when they play.
3. And they like to grab pant-legs.
Info on ... Pugs and why they crawl on their bellies
http://winniewong.typepad.com/shelby/200 ...
