expression
it takes one to know one; a thief knows a thief; the wolf knows what the ill beast thinks
Proverb meaning that people of the same kind, especially those with similar vices or expertise, understand each other best. Often used when someone's insight into another's bad behavior reveals their own similar nature.
彼が詐欺の手口をすぐに見抜いたのは、まさに蛇の道は蛇だね。
He spotted the scam right away—it takes one to know one, I guess.
「蛇の道は蛇」というから、彼の悪巧みはお見通しだ。
As the saying goes, 'a thief knows a thief,' so I can see right through his schemes.
A similar proverb meaning 'birds of a feather flock together' or 'like feels for like,' but with a more sympathetic nuance rather than the knowing-one's-own-kind implication of 蛇の道は蛇.
Literally 'a snake knows the way of a snake.' The exact origin is uncertain, but it is a traditional Japanese proverb reflecting the idea that those of the same kind understand each other's ways.