A quick breath during startle response: Why?

[ppppparker]

Have you noticed this or do you do this ever? The instant someones surprised about something they take a quick breath in. Why does this happen, ..and also,
Is there some word that describes this? a word that describes that reflexive aspect of being startled? Also did Shakespeare have any nice descriptions of the act of being surprised by something?
thanks

 

[Silicon Waffle]

I don't remember whether or not I am breathing when I am being surprised or watching a horror scene.

 

[Sophia]

Maybe it's your body taking in oxygen in case you had to fight or flight.

 

[jackwhirl]

Winding up for a good scream? (In both senses of the word!)