One day Parvati went to bathe in the Mandakini river.with her attendants, Jaya and Vijaya. After bathing, the great goddess's color became black because she was sexually aroused. After some time, her two attendants asked her, "Give us some food. We are hungry." She replied, "I shall give you food but please wait." After awhile, again they asked her. She replied, "Please wit, I am thinking about some matters." Waiting awhile, they implored her, "You are the mother of the universe. A child asks everything from her mother. The mother gives her children not only food but also coverings for the body. So that is why we are praying to you for food. You are known for your mercy; please give us food." Hearing this, the consort of Shiva told them that she would give anything when they reached home. But again her two attendants begged her, "We are overpowered with hunger, O Mother of the Universe. Give us food so we may be satisfied, O Merciful One, Bestower of Boons and Fulfiller of Desires."
Hearing this true statement, the merciful goddess smiled and severed her head. As soon as she severed her head, her head fell on the palm of her left hand. Three bloodstreams emerged from her throat; the left and right fell respectively into the mouths of her flanking attendants and the center one fell into her mouth. After performing this, all were satisfied and later returned home. (From this act) Parvati became known as Chinnamasta.
In this painting here, Chinnamasta has cut off her own head with a sword. Her left hand supports her head, and the right hand holds the sword with which she cut it off. Three jets of blood gush from her neck: one stream enters the mouth of her severed head; the other two jets enter the mouths of two female companions.
The self-sacrificing, nourishing intent of Chinnamasta is emphasized by Pratapaditya Pal: "The obvious implication here is of primal sacrifice and renewal of creation. The goddess sacrifices herself, and her blood, drunk by her attendants, renews or resuscitates the universe..Therefore beheading her own head is a temporary expedient to provide food and appears to be a more sanguinary manifestation of the goddess as Shakambhari (she who bears vegetables) and Annapurna (she who is full of food).
This description by Nitin Kumar, Executive Editor, Exotic India.
Pal, Pratapaditya, Hindu Religion and Iconology (Los Angeles: Vichitra Press, 1981)
Kinsley, David, Tantric Visions of the Divine Feminine( New Delhi, Motilal Banarsidass, 1998).