The French They Never Taught You 23: bouche, feuille
In your elementary French class, you learn the word for mouth: la bouche. And this word is feminine. It's la bouche, not le bouche. However, the expression "word of mouth" is masculine: le bouche à oreille. After you've been saying la bouche for years, you will be tempted to say "la bouche à l'oreille." But the expression is in fact le bouche à oreille. Another expression where bouche seems to suddenly become masculine is faire du bouche-à-bouche à quelqu'un: to give someone