Brain freeze" is the pain sometimes inflicted by devouring something cold like ice cream or a cold beverage, often very quickly.The reaction is (obviously) triggered by the cold ice cream or beverage; coming into contact with the roof of the mouth. It triggers nerves that give the brain the impression of a very cold environment. To heat up the brain again, blood vessels start to swell, which causes the headache-like pain for approximately 30 seconds.
The temperature change in the roof of the mouth has to be rather drastic; this is why brain freeze often occurs on warm days.
The pain can be relieved by putting the tongue to the roof of the mouth, which logically will heat it up.
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