The story of demons Chanda Munda is mentioned in the Devi Mahatmya. They were the assistants of demon kings Shumbha and Nishumbha. The propitiated Brahma through intense austerities and gained the boon that they could never be slain by a man. They considered a woman too weak to fear.
Armed with a powerful boon, they created havoc in the universe. The caused destruction and hardship on earth. They trampled the innocent and they destroyed the nature.
Finally, they came face to face with Goddess Durga. Seeing the cruelty inflicted by Chanda Munda on her children, the face of Maa Durga became dark with rage.
At that moment, Goddess Kali jumped out from her right eyebrow. The face and appearance of Goddess Kali was terrible. Merely her sight caused fear and havoc in the army led by Chanda and Munda. Many of the demons in the army fell dead out of shock and fear. Those that did not die of fear ran away from the battlefield.
Goddess Kali appeared emaciated with sunken eyes, drooping breasts, a skeletal body, and four arms. She was wearing a long garland of severed heads, as well as a serpent necklace around her neck. Another snake, which was coming out of and entering her navel, was tied around my hip. Her deformed breasts heightened her grotesque and frightful image. The sunken cavities of her body sharply contrasted with those of the graceful Durga.
Those demons in the arm of Chanda and Munda that tried to attack Goddess Kali were killed by her with ease.
Goddess Kali then engaged in a ferocious fight with Chand and Munda. But they powerless and clueless before the might Kali. Soon, Goddess Kali cut off the heads of the demons Chanda and Munda and presented them to the Goddess Durga.
From that day Goddess Kali was also known as Chamunda.
Maa Kali then returned into Durga.