Why will a dog lick the carpet?

Answer 1

As far as can be determined dogs can detect "food" or "food-like odours" of any description at levels below human perception. If at anytime food has been dropped on the carpet, someone who had stepped on food had later stepped on the carpet, or the dog had drooled on the carpet while eating food, the dog will assume that there is still food there and will attempt to get it. In addition the dogs discrimination as to what is food and not-food is a lot different than ours and it becomes interested in materials we would describe as just plain disgusting.

Scientifically dogs have olfactory (smelling) abilities several thousand times better than humans. Their brains are wired to use this data input like we would use vision. Some researchers speculate that dogs noses "see" odours like glowing colours. The carpet in question might well be a riot of "smell-colours" from every chip or sweaty foot that has ever been on it.