In case you are wondering how this happens, it's because when the flask was corked, the steam that was generated by the boiling of the water had taken the place of any air that had been in the flask. As the flask cools, the steam condenses back to water, leaving a (partial) vacuum inside the flask. This lowers the boiling point of the water inside to less than normal body temperature. I don't know what the acutal numbers would be, for the temperature and pressure, and i leave that to you to find out