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.
They just LOOK like they’re covered in warts. Human warts happen when a person comes into contact with one of the hundred human papilloma virus subtypes.
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.