Futakuchi-onna

Multiple tale-variants account for the origin of the second mouth. The prototypical narrative recorded in English-language reference retellings describes a stingy miser who marries a woman who appears not to eat; when his rice stores steadily decline he spies on her and discovers that the back of her head parts to reveal a second mouth whose hair acts like tentacles to feed it (the mouth thus explains the missing rice). Other variants in collected summaries attribute the condition to an accidental head injury (for example, a wound inflicted by an axe that never heals and becomes a mouth) or to supernatural revenge in which the spirit of a neglected or starved child inhabits the woman and manifests as the second mouth.

Tales depict the woman as outwardly ordinary but with a second mouth on the back of her head beneath her hair; in story descriptions the skull at that location is said to split open to form lips, teeth and a tongue, producing an apparently functional second mouth. In some variants the woman's hair is described as moving like tentacles or "a pair of serpents," and the hair is said to assist the rear mouth in taking food.

In folktale accounts the second mouth is functional and vocal: it mumbles spiteful or threatening things and demands food, and if not fed it is described as screeching and causing the woman pain. Stories describe the rear mouth consuming large amounts (in one summary quoted as "twice" what the front mouth would) and—together with the hair acting as appendages—taking food directly from storage or meals. The mouth's voice and appetite are presented in tales as distinct behavioral traits that reveal the woman's hidden condition.