Possible Clues:

• "Seriously!"
• 'I'm serious!'
• 'I'm not kidding!'
• 'I know it sounds weird, but it's true!'
• 'Seriously!'
• 'I'm being serious!'
• 'Honest, it's true!'
• "Honest, it's true!"
• "I'm serious!"
• Sarcastic reply to the obvious