The phrase "opening one's mouth" refers to speaking or expressing oneself. Some antonyms for this phrase could include remaining silent, keeping quiet, refraining from speaking, or holding one's tongue. These actions may be intentional or involuntary, reflecting a desire to avoid conflict or simply a lack of things to say. In some contexts, closing one's mouth or staying silent can be a sign of wisdom, restraint, or self-discipline, while in others it may suggest cowardice or a lack of confidence. Ultimately, the antonyms for "opening one's mouth" point towards the complexity of human communication and the diverse ways in which we express ourselves.