Related Clues:

• "Hmm, I didn't know that!"
• 'Colour me scandalised, certainly'
• Head scratcher's remark
• "No kidding"
• "I don't know" lead-in
• Crikey!
• Turn signal, on a horse
• Sense organ's sound, for example, producing surprised reaction?
• "___-whiz!"
• Surprised expression
• How British draw attention to one, for example
• 'No kiddin'!'
• 'Well, well, well!'
• "Who knew?"
• 'Didn't know that!'