On the table is a bar of chocolate. A person is not hungry, but imagining how chocolate melts in his mouth, he feels his mouth fill with saliva – there is a craving for sweets and now his hand reaches for the dark brown tile. How does this indescribable craving for sweets arise? There are several reasons. First, a person can not do anything about it, because the preference for sweet is natural – even newly born babies respond to a sweet liquid with a smile.