尻尾しっぽを掴つかむ

expression, godan verb (-mu)

have something on someone; catch someone out; get evidence on someone

Idiomatic expression literally meaning 'grab the tail'. Used when you find a weakness, mistake, or secret that gives you leverage over someone.

• 彼かれの不ふ正せいの尻尾しっぽを掴つかんだ。

  I got evidence of his wrongdoing.

• 相あい手てのミスの尻尾しっぽを掴つかんで、交こう渉しょうを有ゆう利りに進すすめた。

  I caught the other party's mistake and used it to gain an advantage in the negotiations.