Rare as Hen's Teeth - What does it mean?
What are Hen’s Teeth, and where do you find them?
This very common English idiom is actually one of the easiest ones to understand, even though it may not seem it at first.
We use it when we want to demonstrate that something is almost impossible to find. So hard to find in fact, that you would have more chance of finding a hen with teeth. Which as any school child knows, is impossible because chickens do not have teeth. No matter what they try and tell us in those cartoons.