Related Clues:

• Act passionately
• Gasp, perhaps
• Change, chemically
• Say "wow!", e.g.
• Overdo it on stage
• Respond
• Act badly
• Make a face, say
• What 14-Downs do
• Not play it straight
• Be a ham in 'Hamlet'?
• Flinch, e.g.
• Flinch, perhaps
• Act broadly
• Show surprise, perhaps