Women using poison to murder their husbands is an old trope – one going back as far as Claudius's poisoning, which implicated his wife Agrippina. "Arsenic Annie" Nannie Doss saw off four husbands, as well as most of her family, in the span of four decades (she confessed to the murders in 1954). And now a Brazilian woman may soon be added to this pantheon of gloom. Although this alleged attempted homicide was unsuccessful, the method will certainly go down in history: she allegedly put poison in her vagina, and invited her husband to perform oral sex on her. The man became suspicious while down south, surprised by an "unusual smell". He took her to hospital, where the poison was found.

There is something particularly intriguing about using a method of murder that involves pleasure. It's also completely stupid, as vaginas are absorbent and the woman would have probably killed herself in the process. But no matter, a lethal love tunnel adds to the fascinating mythology of sex and death in the lady garden.

Paranoid fantasies about ladies' bits are nothing new. Vaginas seem dark and mysterious, and produce strange liquids. Its secretions form the basis of the belief that women are unclean, indeed ritually so. As the South Park character Mr Mackey said: "I just don't trust anything that bleeds for five days and doesn't die." And yet pleasure – and most importantly life – also emanate from it.

This "dark power" inspired folklore. It was believed at various points in history that menstrual blood was semen "gone bad", that women took men's life-force through their vaginas, that the female orgasm should be prescribed for anxiety disorders, and that some vaginas came laced with teeth that could castrate a man. Indeed, the myth of the vagina dentata – meaning toothed vagina – can be found in many different cultures, from Greek mythology to the Chaco and Guiana tribes of South America. Its message can be subtly different, depending on where it originated from: it either says that penetrative sex is dangerous, that women are evil temptresses bent on male castration, or that men should not rape women, or suffer the consequences.

This latter threat was actually realised with the invention of Rape-aXe, an anti-rape female condom invented by Sonnet Ehlers in South Africa in 2005. The Rape-aXe is a latex sheath embedded with sharp, inward-facing barbs that would dig into the attacker's penis, causing excruciating pain.

Of course the threat of castration, whether real or imagined, should not be the motivation for men not to rape. The mythology surrounding vaginas harm women more than help them. Many women would not actually want to put someone off oral sex with the possibility that it may be a poisoned furry chalice (women are also not more likely to be a poisoner than men: the overwhelming number of convicted poisoners are men). As long as women are made to feel powerless, those powerful myths will be embraced and used to protect ourselves by turning us into witches, poisoners or sirens. But these myths only perpetuate fear, distrust and disgust of female genitalia. There are other ways to bite back.