糸いと口ぐちを開ひらく

expression, godan verb (-ku)

find a clue; get a lead; make a beginning

Used when a small hint or starting point leads to solving a problem or starting something. Often implies a breakthrough after a dead end.

• 警けい察さつはようやく事じ件けんの糸いと口ぐちを開ひらいた。

  The police finally found a clue to the case.

• 彼かれの一ひと言ことが研けん究きゅうの糸いと口ぐちを開ひらいた。

  His single remark provided a starting point for the research.