cāo gē rù shì
比喻深入了解对方，找出其纰漏，又以对方的论点来批驳对方。
明 胡应麟《少室山房笔丛 史书占毕一》：“论者以柳操戈入室，弗察者又群然和之。然则文之工者，伤理倍道，皆弗论乎！”
操戈入室作谓语、定语；用于言辞、学问等。
attack somebody with his own spear in his own house--turn somebody's words or argument against himself
