Incase you didn't know. I got this through e mail and thought I would pass it on to you.
Could nuking your water be dangerous?
I feel that the following is information, that anyone who uses a microwave oven to heat water should be made aware of. About five days ago my 26-year old son decided to have a cup of instant coffee. He took a cup of water and put it in the microwave to heat it up (something that he had done numerous times before). I am not sure how long he set the timer for but he told me he wanted to bring the water to a boil. When the timer shut the oven off, he removed the cup from the oven. As he looked into the cup he noted that the water was not boiling but instantly the water in the cup "blew up" into his face. The cup remained intact until he threw it out of his hand but all the water had flew out into his face due to the buildup of energy. His whole face is blistered and he has first and second degree burns to his face, which may leave scarring. He also may have lost partial sight in his left eye. While at the hospital, the doctor who was attending to him stated that this a common occurrence and water (alone) should never be heated in a microwave oven. If water is heated in this manner, something should be placed in the cup to diffuse the energy such as a wooden stir stick, tea bag, etc. It is however a much safer choice to boil the water in a teakettle.
This sounds like an urban legend but it isn't. The issue is that a very clean cup has no nucleation points to initiate the boiling, and the water can become superheated beyond the usual boiling point. If mechanically disturbed in this state, like inserting a spoon or adding your cocoa mix, all of the stored energy can be released all at once. Not all the water turns to steam, only a small fraction, but it can throw the remaining hot water a significant distance.