Related Clues:

• Practice tit for tat
• Have a poor poker face
• Gasp, perhaps
• Change, chemically
• Say "wow!", e.g.
• Respond
• Make a face, say
• Fight back
• Flinch, e.g.
• Flinch, perhaps
• Show surprise, perhaps
• Flinch or blink, say
• Smile, e.g.
• Block a punch, e.g.
• Get revenge