When a young monster by the name of Harvey hears his parents discussing the new baby that’s due soon, his father refers to it as “another mouth to feed.”  Harvey misinterprets this to mean that the new arrival will be just a giant mouth, and his spends the rest of the book stressing over what that will be like, only to discover when mom does return from the hospital that it’s not just a mouth, but a regular monster with all the usual features, including three eyes.  A page in the back of the book describes what an idiom is, and the meaning of this particular idiom.  I’m not a fan of the artwork in the book, and the plot seems a bit blah.  There are better things out there to teach idioms.