(11)轻微的咔嚓声打断了程海的思路，他的眼光突然严峻起来：桥头的树下，一个十三、四岁的男孩嘴里叼着一根香烟，起劲地拨弄着打火机。

(11) A slight cracking sound interrupted Cheng Hai’s train of thought, [and] his expression suddenly turned stern. Under a tree at the other end of the bridge, a boy of about thirteen or fourteen years had a cigarette dangling from his lips, enthusiastically flicking a lighter.