I read this children’s book in the 1970s, but the book could have been older than that. A girl gets a unicorn horn from somewhere (possibly an antique store or a relative), and whenever she holds it, figures of speech become literal. I remember being freaked out by a woman whose tongue literally began flapping at both ends. This may have been only one of several magical things that happened to the girl over the course of the book, but it’s the only one I remember.