Possible Clues:

• Question that introduces doubt
• End of an incredible statement
• Second-guesser's question
• Doubt-raising question
• Doubt-raising question, and a hint to the transformation applied to each starred clue's answer
• Doubt-introducing question
• '... you sure about that?'
• Doubt-invoking question end
• End of an uncertain statement
• Question that leaves an opening for doubt