A Futakuchi-onna is a legendary Japanese monster, or yokai. The name Futakuchi-onna means "two-mouthed woman," and as the name suggests, this type of monster has a second functional mouth in the back of her head. Futakuchi-onna appear throughout Japanese folklore, where the second mouth is usually the result of a curse or other supernatural causes.

The second mouth of a Futakuchi-onna must eat, often much more than a regular mouth. If it is not fed, it may begin to mumble and threaten the Futakuchi-onna, and it may become painful and begin screaming. The hair of a Futakuchi-onna is sometimes said to become tentacle-like, picking up the woman's food from her plate and feeding the second mouth.

In many stories, a woman becomes a Futakuchi-onna after letting her stepchild starve to death; in such cases, the dead child's spirit effects the curse and may even reside in the woman's body. In other tales, Futakuchi-onna are the wives of misers, who become cursed as a result of their husbands' stinginess. In one story, a woman becomes a Futakuchi-onna after her husband strikes the back of her head with an axe. Instead of healing, the wound becomes a second mouth that must be fed.

One of the most well-known Futakuchi-onna stories tells of a man who chose his bride because she never ate a thing. As a miser, he could not bear the thought of feeding another mouth besides his own, so the fact that his wife never ate was a huge attraction. However, he soon noticed that his stores of rice were mysteriously being depleted. When he spied on his wife one day to see what was going on, he discovered that she was a Futakuchi-onna. He saw a gaping mouth open in the back of her head, and when she unbound her hair, it shoveled huge quantities of rice into the second mouth.