Ice-nine is a fictional substance created by author Kurt Vonnegut in his novel "Cat's Cradle." It is a form of water that freezes at a temperature of 114.4 degrees Fahrenheit (46.3 degrees Celsius) and has the ability to cause other water to freeze upon contact. This unique property makes it a dangerous material, as it could potentially freeze all the world's water. In the story, ice-nine symbolizes the destructive potential of scientific advancements when misused. The concept serves as a cautionary tale about the consequences of human hubris and the ethical responsibilities that come with scientific discovery.