«فَلَا تَقُلْ لَهُمَا أُفٍّ»
Do not even say “uff” to either of your parents.
The text prohibits a minor expression of hurt. The prohibition of greater mistreatment is understood through dalalat al-nass, recognizing the readily understood basis of the prohibition: harming one's parents. A legal inference is not always based on a matching word; a more serious instance may fall within what the text clearly conveys.