A crocodile, when presented with food, tears are released. Most of us think that crocodile is showing of sympathy for his potential victim. In fact, the crocodile is not at all guilty for the victim. It is just that the parasympathetic nerve ﬁbres to the crocodile’s lacrimal (tear) glands get activated at the same time as the nerve ﬁbres to the salivary glands.
Therefore, when crocodile ﬁnds some tasty food, not only its mouth begins to water with saliva, but it also starts releasing tears. So the “crocodile tears” in English dictionary means as a fake tears or expressions of sorrow that are insincere.
The arrangement in human is different. All three major salivary glands as well as the lacrimal gland are innervated by different branches nerve, the facial nerve. Sometimes when a man’s facial nerve is injured, it regenerates only imperfectly. Some of the regenerating nerve, which originally supply to the salivary glands, get slightly misdirected and supply to lacrimal glands. Such a man also releases ‘crocodile tears’ at meal time.
Source: RL Bijlani; Understanding of medical Physiology 4th edition