This video shows what happens when you get the temperature and pressure of a liquid just right...
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So that at first it freezes.
Then it boils.
Then... it does both at the same time?
This (unspecified) liquid appears to have reached its "triple point", where it exists as a solid, a liquid and a gas at the same time.
Liquids start behaving strangely around this temperature and pressure. For example, below the triple point pressure, when ice is heated it turns directly into water vapour without first becoming a liquid.
Which is pretty neat.
