The demon (asura) Bhasma (ashes) had gained the favor of Shiva that everyone he touched with his index finger would burn to ashes.
Bhasmasura, who had an eye on Parvati, wanted to try this right away by touching Shiva. Shiva fled, Bhasmasura pursued him. Shiva hid with Vishnu, who took the form of a woman, Mohini.
When Bhasmasura appeared, he was immediately in love and proposed marriage to her. Since she liked to dance, she demanded that he is able to dance exactly her dance movements. He agreed.
When Mohini danced a pose in which her index finger was placed on her head and Bhasmasura imitated it, he was burned to ashes.