A light from the shadows shall spring!

焼け木杭に火がつく
(Yake-bokkui ni hi ga tsuku; “Fire catches on a burned stick”)

Definition:

A former relationship that was cut off is easy to reestablish. On meeting an old friend or lover, you often quickly end up talking as if you’d never been apart, in contrast to the relatively slow intimacy of meeting someone wholly new. The comparison is to how a stick of charcoal – which has been burned once – is easy to light afire again.

Breakdown:

We begin with the intransitive verb 焼ける (yakeru), “to burn,” in prenominal form. This allows it to precede and modify the compound noun 木杭 (bokkui), “wooden stake,” which is marked by particle に (ni) as the location of the verb つく (tsuku), “to catch (fire).” The subject of this verb is, unsurprisingly, the noun 火 (hi, sounds like “hee”), “fire,” and is marked as such by the particle が (ga).

Notes:

Some variants stress the ease of the rekindling, e.g. 焼け木杭には火が付き易い (yake bokkui ni wa hi ga tsukiyasui). Others replace 焼ける with 燃える (moeru), “to burn,” without significant change in meaning. Supposedly bokkui is a phonetic alteration of 棒杭, boukui, where 棒 means “staff,” and it is still possible to write bokkui as 棒杭. However, in modern writing, 木杭 is by far the more common rendering.

Example sentence:

「十五周年の同窓会の二次会が終わったら、沢尻さんと峰くんが楽しそうに隣りの公園で話しているのを見かけた。焼け木杭に火が付くってやつね」

(“Juugoshuunen no dousoukai no nijikai ga owattara, Sawajiri-san to Mine-kun ga tanoshisou ni tonari no kouen de hanashiteiru no wo mikaketa. Yake-bokkui ni hi ga tsuku tte yatsu ne.”)

[“At our 15-year class reunion, after the after-party ended, I happened to spot Sawajiri and Mine talking in the neighboring park. They seemed to be having a good time. I guess that’s what you call ‘rekindling an old flame.’”]