What causes "brain freeze?"

[WCCO-TV, May 27, 2015] On a warm day like today, some ice cream sounds like a good idea. But eat it too fast and you could get that cold headache -- brain freeze. So what causes that pain in your head from eating cold food too fast? That's the Good Question WCCO-TV put to Abbott Northwestern Hospital interventional neuroradiologist Dr. Yasha Kayan.