Related Clues:

• Exception to the rule
• Hole in one, e.g.
• Curious thing
• Peculiar thing
• Hole-in-one, e.g.
• 'Believe It Or Not!' item
• Rare bird
• It doesn't happen often
• It hardly ever happens
• Collector's item
• Curio
• Unusual item
• Something unusual
• Aberration
• One-of-a-kind find, to Caesar