マウスピースに口を付けるput one's hand over mouthpiece: 受話器{じゅわき}を手でふさぐ[に手を置く]put one's hand over someone's mouth: 自分{じぶん}の手で(人)の口をふさぐplace one's hand over the mouthpiece: 受話器{じゅわき}を手で覆う