The cold stimulus headache, better known as ice cream headache or brain freeze, starts on the roof of the mouth. This episode explains how freezing food on the richly vascular palate makes blood vessels constrict and then rapidly swell again, a rebound vasodilation that sets off dense pain receptors. The signal travels along the trigeminal nerve, which also serves the forehead, and the brain refers the pain to the wrong place, the same mechanism that sends heart attack pain to the arm. An alternative theory points to the anterior cerebral artery flooding the brain with warm blood, raising pressure inside the rigid skull until the vessel constricts and the pain stops.

The same neurovascular wiring is implicated in migraine aura and throbbing pain. A study in the journal Headache found 17 percent of migraine patients got a headache from one swallow of ice cream, compared with 46 percent of students. In another study, eating ice cream in under five seconds produced headaches in 27 percent of people, versus 12 percent for those who took more than 30 seconds, and children are more prone than adults. The first written account came from Patrick Brydone in the 1770s, describing a British naval officer in Sicily who spat out ice cream with a horrid oath.

• Why cats get brain freeze, and the whisker sensitivity of their trigeminal nerve
• The phrase ice cream headache in 1937, brain freeze in this sense in 1986, and 7-Eleven’s trademark
• A competitive ice skater who triggered it by breathing the cold air above the rink
• Awake neurosurgery patients who felt brain freeze when a drill reached the inner table of the skull
• Pressing the tongue to the palate to rewarm the vessels