You've just dug into that delicious bowl of ice cream when it strikes — a sharp, stabbing pain in the middle of your skull. Thirty seconds later, it's gone. You've just been hit with brain freeze.
Brain freeze occurs when something really cold touches the soft palate on the roof of your mouth, causing the blood vessels there to suddenly constrict. As warm blood starts to flow through them again, the vessels dilate, causing receptors to send a pain signal to your brain. The message is sent through the nerve that is responsible for feeling in your face, so your brain thinks the pain is coming from your forehead — which is what causes that brief but intense headache sensation.