expression, godan verb (-ru)
start a debate; get the ball rolling; fire the first shot; start a conversation
Idiomatic expression meaning to initiate a discussion, debate, or action; often used when someone takes the lead in a group setting.
彼が口火を切って、会議が始まった。
He started the debate and the meeting got underway.
誰かが口火を切らないと、話が進まない。
If someone doesn't get the ball rolling, the conversation won't move forward.