捯线头

Traditional (Taiwan): 捯線頭

dáoxiàntóu ㄉㄠˊ ㄒㄧㄢˋ ㄊㄡˊ

    • to trace something back to its cause or origin

Character by character

Saying俗语俗語

Idiom惯用语 · Rarely used now

Literally
hauling in the thread end
Meaning
To trace something back to its cause or origin, as when you pull in a thread hand over hand. Used for investigating how a matter began.

Sources