Human beings are born with several instinctive fears, each of which can be traced back to maximizing our furry ancestors' chances of surviving and passing on their genes. Losing your grip on a tree branch would have made you a dead monkey — thus, our fear of falling. Fear of snakes is also understandable, considering that many species are poisonous and others would have liked to eat early hominids. And, of course, given the male tendency to try to hump everything with a conveniently sized hole, there's the fear of putting your penis somewhere it won't come out of again. Sex is aggressive and penetrative by nature; the thought of being caught in a situation where you've committed your forces but are unable to pull out is inherently terrifying — besides which, getting back less than you put in would definitely remove you from the gene pool.
No wonder the vagina dentata is such a universal motif, showing up in myths originating everywhere from the Indian subcontinent to the Plains Indians. (It's not true that the idea originated with Mrs. Freud's little boy: While the good doctor did talk about castration anxiety in general, he never tackled the fanged furbox.) However, the interpretation of this symbol has changed over time. In the past, the woman with teeth "down there" was an object of fear; today, the vagina dentata approaches a symbol of female empowerment.
Like other human universals, the vagina dentata is born from our corporeal experience. Sex is an eternal choice between Scylla and Charybdis: we're compelled by biology to do it, but it could be humiliating or damaging. Screwing makes us look ridiculous. We get sleepy afterward. Trying to obtain a mate is an ego-destroying experience that reminds us where we stand on the social ladder. Even though people rationally know that men can survive the loss of their genitalia, castration in these myths is universally associated with death.
No wonder, then, that a common motif in toothed-cootchie mythology is that the masculine part of the female must be removed to socialize her. (Take, for example, the delightful Native American tale "How Coyote Made
The theologian Tertullian noted that "woman is the gate to hell."
Woman Useful by Breaking the Teeth in her Vagina.") We're all familiar with the frightening symbols of patriarchy — sky-fathers hurling lightening bolts, Bible-thumping televangelists, Wilford Brimley shilling oatmeal — but feminine symbols also hold power. In a patriarchal society, this is a power that needs to be tamed. The Nandi of Africa, for instance, justify female genital mutilation by explaining that the clitoris is a "tooth" that must be excised.
The Judeo-Christian tradition is no exception to this. In the apocryphal Book of Tobit, Sarah was haunted by the demon Asmodeus, who kills each of the seven men who try to marry her. To paraphrase Anne Carlisle's immortal line from 1982's Liquid Sky, she's a murderer who kills with her cunt. The killing spree is halted by the archangel Gabriel, who instructs Sarah's eighth husband, Tobias, to perform a magical ritual that drives the demon out. In the morning, Tobias is still alive and the dangerous woman, again made safe, is presumably free to make breakfast.
This sort of misogyny was appropriated by the medieval church. The theologian Tertullian noted that "woman is the gate to hell," and the artistic motif of the "hell mouth" — the gaping vagina as the literal door to damnation — gave his words concrete form. Late-medieval people believed witches could render men impotent without even touching them. In one legend from the period, a witch keeps her collection of penises in a bird's nest; when a villager comes to get his cock back, she tells him to take any one he likes, but not the biggest and fattest, because that one belongs to the parish priest. Set against the demimonde of witches and devils with their all-consuming cunts is the Virgin Mary, immaculate and without sin, looking down from the church vaulting, safely enclosed in her vaginal mandorla.
The contrast between virgin and witch/whore highlights another aspect of the vagina dentata mythos: The sexually voracious woman who refuses to accept her passive role but instead consumes her lover like a praying mantis.