Vagina dentata

Vagina dentata (Latin for "toothed vagina") describes a folk tale in which a woman's vagina is said to contain teeth, with the associated implication that sexual intercourse might result in injury, emasculation, or castration for the man involved. The topic of "vagina dentata" may also cover a rare medical condition affecting the vagina, in which case it is more accurately termed a "vaginal dermoid cyst".
In folklore.
Such folk stories are frequently told as cautionary tales warning of the dangers of unknown women and to discourage rape.
The psychologist Erich Neumann wrote that in one such myth, "...a fish inhabits the vagina of the Terrible Mother; the hero is the man who overcomes the Terrible Mother, breaks the teeth out of her vagina, and so makes her into a woman."
South America.
The legend also appears in the mythology of the Chaco and Guiana tribes of South America. In some versions, the hero leaves one tooth.
North America.
The Ponca-Otoe tell a story in which Coyote outwits a wicked old woman who placed teeth in the vaginas of her daughter and another young woman she kept prisoner, in order to seduce, kill, and rob young men. Coyote kills the woman and her daughter but marries the other young woman, after knocking out the teeth in her vagina "except for one blunt tooth that was very thrilling when making love".
Hinduism.
In Hinduism, the "asura" Andhaka, son of Shiva and Parvati (but not aware of it), is killed by Shiva when he tries to force the disguised Shiva into surrendering Parvati. Andhaka's son Adi, also an "asura", takes the form of Parvati to seduce and kill Shiva with a toothed vagina in order to avenge Andhaka, but is also slain.
Ainu and Shinto legends.
The Ainu legend is that a sharp-toothed demon hid inside the vagina of a young woman and emasculated two young men on their wedding nights. Consequently, the woman sought help from a blacksmith who fashioned an iron phallus to break the demon's teeth.
The legendary iron phallus is considered to be enshrined at the Kanayama Shinto Shrine in Kawasaki, Japan, and there the popular Festival of the Steel Phallus is held each spring. Also, prostitutes once considered that praying at that shrine protected them against sexually transmitted diseases.
Māori mythology.
In Māori mythology, the trickster Māui tries to grant mankind immortality by reversing the birth process, turning into a worm and crawling into the vagina of Hine-nui-te-pō (the goddess of night and death) and out through her mouth while she sleeps. His trick is ruined when a laughs at the sight of his entry, awakening Hine-nui-te-pō, who bites him to death with her obsidian vaginal teeth.
Western Asia.
Arabs from South-Eastern Iran and islands in Strait of Hormuz have a legend about Menmendas, a creature that looks like a beautiful young woman with spikes on her thighs. She walks in the coastal mountains with a small box of jewels and attracts every man on her way. Menmendas goes with an attracted man into an empty house, puts the box of jewels under her head and lies down with spreading legs. If the man understands who this woman is, he can cast a fistful of sand in her eyes and run away with the box. If the man gets attracted and turned on, the woman gathers him into half-and-half by her legs.
Metaphorical usage.
In her book "Sexual Personae" (1991), Camille Paglia wrote: "The toothed vagina is no sexist hallucination: every penis is made less in every vagina, just as mankind, male and female, is devoured by mother nature."
In his book "The Wimp Factor", Stephen J. Ducat expresses a similar view, that these myths express the threat sexual intercourse poses for men who, although entering triumphantly, always leave diminished.
Medical.
In rare instances, dermoid cysts (a type of tumor) may grow in the vagina. Dermoid cysts are formed from the outer layers of embryonic skin cells. These cells are able to mature into many different types of tissues, and these cysts are able to form anywhere the skin is or where the skin folds inwards to become another organ, such as in the ear or the vagina. However, when dermoid cysts occur in the vagina, they are covered by a layer of normal vaginal tissue and therefore appear as a lump, not as recognizable teeth.