The enchanted harmonica with the painted “M” has a special significance in Echo. We eventually learn that “M” stands for messenger, and the harmonica seems to a carry of message of consolation and self-empowerment wherever it goes.

The harmonica’s status as an instrument that is sometimes perceived as vulgar or silly is directly addressed. In Nazi Germany, the harmonica is looked down on. However, in 1940s America, Hoxie’s Harmonica Wizards elevate the instrument: the very things that make it abhorrent in Germany endear it to an American audience. It makes music youthful, unserious, and fun. It is easily portable, including to the front lines of war, and thus can serve as an accessible, democratic instrument.

Each section of the book has a literal refrain—a song played again and again by its main character. This is Friedrich’s refrain. Friedrich hears his father play this song when he is sad, and it’s a significant way for Friedrich himself to mourn the loss of his mother and the absence of his sister. Although it is a sad song, it brings him comfort and strength as he plays it in preparation for leaving Germany forever.