When someone says this in regard to information, we know that it is from the highest authority. The expression comes from horse racing and has to do with how you can tell a horse’s age from their teeth and not rely on what the owner tells you.
When someone says this in regard to information, we know that it is from the highest authority. The expression comes from horse racing and has to do with how you can tell a horse’s age from their teeth and not rely on what the owner tells you.