if a frog is placed in a container along with water from its own pond, it will remain there, utterly still, while the water is slowly heated up. 

The frog doesn't react to the gradual increase in temperature, to the changes in its environment, and when the water reaches the boiling point, the frog dies, fat and happy.

On the other hand, if a frog is thrown into a container full of already boiling water it will jump straight out again, scalded, but alive