Why you get brain freeze or "ice cream headache" when you drink an icy or cold drink. ?

No-one knows precisely why this is, but people think that it is a form of referred pain.

Referred pain means that you have damage or pain coming from somewhere in your body but you feel it somewhere else.

People who have a heart attack often report feeling pain in their neck or in their left arm - not where their heart is. So in the same way as that, you've got your nervous system fooled into thinking that the pain's coming from somewhere else.

What scientists think is that the nerves in the mouth that are very sensitive to cold temperature accidentally trigger the nerves supplying the front of your head. It then thinks that there's a painful stimulus coming from there, when it's actually coming from your mouth. Another possibility is that when you put very cold things into your mouth, there's a nerve reflex to do with regulating heat and blood flow through your face and head.

It might be that when you put something cold onto the nerves that signal this reflex, it goes into overdrive and the blood vessels temporarily open too much because they think your head is freezing cold. In the same way that a migraine will give you that horrible throbbing headache, perhaps that's why you get that temporary pain right at the front of your head.