Many people have heard the old metaphor about the frog; if you put one in boiling water it will hop out, but if you gradually increase the temperature of the water it will let itself be boiled. It's meant to warn us about slowly developing dangers in addition to obvious ones.
As metaphors go, a boiling frog works. Step into the realm of reality and the metaphor breaks down. Dr. Victor Hutchison, at the University of Oklahoma, dispelled the myth when he studied frogs' reaction to temperature changes in water. He followed the procedure outlined for a proper frog-boiling; put a frog in cold water, and gradually warmed the water up. (He stopped well before the boiling point.) The frogs most definitely did jump out when the water got too warm for them. So that aspect of the metaphor breaks down.
What about the other aspect? If we want to get really gruesome, we can discuss what happens when you throw a frog into boiling water. No one has done this as an experiment, but scientists are pretty sure they know what will happen if someone did. Getting dropped into boiling water would be serious trouble for a human, and we have nice thick skin and quite large legs. The surface of the body parts that were exposed to the water would be damaged or destroyed, but we'd have enough muscle mass to get out of the water, provided the edge of the container was close and we didn't go into shock. A frog is not nearly as big as we are. The boiling water would destroy its muscles to the point where it could not hop out and would die in the water.
So the real story should be the exact reverse of the "fact" that's so often quoted. Put a frog in some cold water and heat it up slowly, and the frog will hop out. Drop a frog in boiling water and it will be boiled alive. Is it me, or does that sound even scarier?