SABUK, Gangwon Province -- “Never kick a lump of used coal briquette; has your heart ever burned for someone?” reads one of the most beloved Korean poems by poet Ahn Do-hyun. The resonance of this three-line-stanza poem in Korean draws its depth from the commonplace “yeontan” -- the perforated, cylindrical briquettes that fueled the hearths of most Korean households in the mid- to late-...