hen's tooth

Example of a jocularly non-existent phenomenon, as many birds lack any teeth (having developed a bill instead). Compare horsefeathers and when pigs fly.

• "as rare as a hen's tooth"
• "Indeed, many of the Dutch in Pernambuco were won over to the Church of Rome, ‘whereas converts from Catholicism to Calvinism were as rare as hens’ teeth’."

• rocking horse shit
• black swan
• hen's tooth
• lightning in a bottle
• one in a million
• rara avis
• rare bird
• rarity
• rocking horse shit
• unicorn

• unobtanium