To children, non-native English speakers, and anyone who confronts a fixed expression for the first time, they can be baffling. A fixed expression is a little like a secret code that allows access to a club that not everyone can enter. It’s a phrase that has a very specific meaning that can’t be expressed any other way and also can’t be deduced just by considering the sum of its parts. Some fixed expressions, like “ready, aim, fire” are used so often that the opportunity to turn them into a joke creates another fixed expression. Others, such as “before you know it” or “to tell you the truth” have been around for so long that they function almost as a single word.