Micronutrient deficiencies the body - is a serious thing and can lead to unpleasant consequences. Organism knows this and sends appropriate signals. And the body receives a signal from the brain tries to compensate for disadvantage. Who licks salt. Who gnaws chalk.
This phenomenon is linked to a rather amusing legend. For a long time it was believed that elephants go to die on their mysterious elephant graveyard, because nowhere in the African savannah and jungle can not find the tusks of dead elephants. Well, if not - then go. Can not find - mysterious. Sinned at one time and hunters. Clearly, ivory - valuable material. The answer was the same simple and unpredictable at the same time.
It turns out, the porcupine is essential mineral fertilizing. (It is understandable, as thorns in order keep!) Is particularly acute in the rainy season when the soil washed mineral components. And since they are nocturnal animals, that their fishing has long remained behind the scenes. It was only in the 20th century was able to figure out the mystery of the disappearance of the tusks. A sort of a naturally occurring mineral concentrate.
A good teeth, then prickly. Tusks nibble - it will not slurp grass.