Water can boil and freeze at the exact same moment

At just the right temperature (0.01°C) and very low pressure (about 0.006 atmospheres), water reaches a state called the triple point — where ice, liquid water, and water vapor all coexist together, in equilibrium, in the same container.

Under these conditions, dropping the pressure makes water "boil" (flash-evaporate) and "freeze" almost simultaneously — a process that looks exactly like water boiling and turning into ice at the same time.

This isn't just a lab curiosity with no real use: water's triple point is so precisely repeatable that for decades it served as the official international standard defining the Kelvin temperature scale.

The mechanism: at such low pressure, water molecules escape the liquid's surface into gas (boiling) fast enough that they pull so much heat from the remaining liquid that it freezes — two seemingly contradictory processes driving each other.