'We have given our hair to the witch," they said, "so that she would send you help, and save you from death tonight. She gave us a knife. Here it is. See the sharp blade! Before the sun rises, you must strike it into the Prince's heart, and when his warm blood bathes your feet they will grow together and become a fish tail. Then you will be a mermaid again, able to come back to us in the sea, and live out your three hundred years before you die and turn into dead salt sea foam.