Vagina dentata
Latin for "toothed vagina".
Often crops up as a sexist projection onto women's bodies of men's fear of women's sexuality. Devouring mothers and all that.
Sometimes appears in fiction as an instance of fantastical biology, or a science-fictional body modification or device.
As a rape deterrent, it rather rests on the presumption that men will have access to women's bodies anyhow, and that they will go far enough for a device located in the vagina to make any difference, thereby circumscribing women's inevitable position as victims. And they would also be useless against rape committed with the help of foreign objects, or expose victims to blood-borne contagions should their attackers' skin break.
Examples
Fantasy
- Tanith Lee's "Weasel Bride"
Science-Fiction
- Neal Stephenson's Snow Crash.