Water boils at 212° Fahrenheit (100° Celsius) at standard pressure. If you take a few drops of water and toss them into a frying pan at 212° Fahrenheit or above, therefore, the water will start to boil. The water makes a sizzling sound as it rapidly evaporates and steam shoots out of the pan.
But sometimes, that doesn't happen. Sometimes, water droplets form in the pan and remain there, not boiling off.
Now I Know asks Why is that?