expression, godan verb (-ku)
open one's mouth (to talk); start to tell
Used when someone begins to speak, often after a silence or hesitation. Can imply revealing something or finally speaking up.
彼はようやく口を開いて、真実を話し始めた。
He finally opened his mouth and began to tell the truth.
会議中、誰も口
During the meeting, nobody opened their mouth.