I've got a mind full of wicked designs
The origin of a futakuchi-onna’s second mouth is often linked to how little a woman eats. In many stories, the soon-to-be futakuchi-onna is a wife of a miser and rarely eats. To counteract this, a second mouth mysteriously  appears on the back of the woman’s head. While no food passes through  her normal lips, the mouth in the back of her head consumes twice what  the other one would. In another story, the extra mouth is formed when a  stingy woman is accidentally hit in the head by her husband’s axe while he is chopping wood, and the wound never heals. Other stories have the woman as a mother who lets her stepchild die of starvation while keeping her own offspring well fed; presumably, the spirit of the neglected child lodges itself in the stepmother’s body to exact revenge.

The origin of a futakuchi-onna’s second mouth is often linked to how little a woman eats. In many stories, the soon-to-be futakuchi-onna is a wife of a miser and rarely eats. To counteract this, a second mouth mysteriously appears on the back of the woman’s head. While no food passes through her normal lips, the mouth in the back of her head consumes twice what the other one would. In another story, the extra mouth is formed when a stingy woman is accidentally hit in the head by her husband’s axe while he is chopping wood, and the wound never heals. Other stories have the woman as a mother who lets her stepchild die of starvation while keeping her own offspring well fed; presumably, the spirit of the neglected child lodges itself in the stepmother’s body to exact revenge.