What is the term for a small or subtle difference in expression or sound?

The term that refers to a small or subtle difference in expression or sound is "nuances." This word conveys the intricate and often slight distinctions that can alter meaning or perception in communication, whether verbal or nonverbal. In the context of language and expression, understanding nuances is essential, as these subtle variations can convey different emotions, intentions, or shades of meaning that are vital for effective interpersonal communication.

The other options represent different concepts that do not relate to subtle differences in expression or sound. For instance, "prolific" refers to producing many works or results, often used in the context of creativity or productivity. "Atrophies" relates to the wasting away or decline of body tissue or an organ due to lack of use or nourishment. "Bequest" refers to the act of leaving money or personal belongings to someone in a will. Each of these terms has its own specific definition and application, distinct from the nuanced differences that are captured by the chosen term.