Myth of the monster head motif
The monster head motif is linked to the Indian legend of the kirtimukha (the Face of Glory), which is told, for instance, in the Skandapurana (chapter 17).
There was once a titan king called Jalandhara who, by means of asceticism, had acquired great powers and ruled the earth as a tyrant. Imbued of himself, he decided to challenge and humiliate Shiva himself. Jalandhara sent Rahu as a messenger to Shiva, asking the Great God to give him Parvati, the goddess Shiva was about to marry. Shiva went into a terrible rage and from the spot between his two eyebrows burst a horrendous demon. He had the head of a lion and an emaciated body devoured by insatiable hunger. When Rahu, the messenger, saw the demon rush at him, he panicked and begged Shiva for protection. After all, he was but a messenger and should not have to endure Shiva’s wrath in place of his master. Shiva ordered the demon to spare Rahu, but the demon was born hungry and his voraciousness had to be satisfied. Shiva suggested that the demon should feed from his own flesh. The demon began to eat his feet and hands; he ate and ate until only his face remained. Impressed by the scene and satisfied by the obedience of the monster, Shiva declared: ‘You will be known, henceforth, as “Face of Glory” (kirtimukha), and I ordain that you shall abide forever at my door. Whoever neglects to worship you shall never win my grace’.