Have you read about the Huldra? It is a Scandinavian mythical creature, very similar to a Siren or a Nymph. The Huldra is a seductress.
She appears attractive and beautiful, sometimes haunting men in their sleep with her charm. However, once a man becomes ensnared by her, she displays a cow’s tail. The Huldra is not a Christian woman, so if a man weds her in the sight of God, she will lose her tail. Also, she will become very ugly and then very strong. What a trade!
It reminds me of the book Dead Blondes and Bad Mothers by Sady Doyle,
“A monster is a supposed-to-be-subjugated body that has become threatening and voracious—a woman who is, in the most basic sense, out of (men’s) control.”
The Huldra is the transformation of a woman, subjugated to man, into a monster who seduces and traps men. The tail? Well, that probably represents the phallus as a symbol of dominance.
Our culture promotes the idea that attractiveness and female sexuality equates to confidence and power. So to take control over the Huldra, she must lose her beauty as well as her tail. The fact that Christian marriage is the cure is no surprise because, in these tales, the divinely appointed role of women is to help men.
In tales of the Huldra, strength makes up for the loss of beauty. For example, in one version of the Huldra, found in Clara Stroebe’s The Norwegian Fairy Book, the Huldra is despised for her ugliness until she shows utility by bending horseshoes with her bare hands.