Possible Clues:

• Feign astonishment
• Convulsive catching of breath
• 'I'm shocked!'
• Breath of wind over top of prairie
• [Mercy!]
• Shocked inhale
• Reaction to a surprise ending, perhaps
• Breathe hard as it's held by the doctor
• Shocked reaction finding Cleopatra's killer after mid-night
• Catch one's breath in astonishment