The expression "rare as a hen's tooth" comes from the fact that chicks in the egg have what is known as an "egg tooth" on their beak which helps them break out of the shell. They lose it almost immediately after hatching. Hence the expression.
The expression "rare as a hen's tooth" comes from the fact that chicks in the egg have what is known as an "egg tooth" on their beak which helps them break out of the shell. They lose it almost immediately after hatching. Hence the expression.