When I was a kid, we had a puppy that started chewing on the edges of a concrete slab. She actually managed to do a little damage - enough so that we finally asked the vet if there might be something wrong. He gave us a calcium supplement for her food and explained that dogs will seek a source of any mineral or nutrient lacking in their diet. I was thinking about this the other day while craving a Nirvana chocolate. So is the conclusion obvious? To what extent might this be true in humans; assuming of course that our vet was correct. If this does happen in humans, how can one tell if a craving is due to a need, or a want? And generally, why do we crave anything if we don't need it? Note that the dog did stop chewing on the concrete almost immediately, as I recall.