‍句中的现在分词短语 complaining of a pain in the forehead 用作状语，表示伴随。类似的用法如：
She goes around complaining about her job. 她到处抱怨她的工作。
An old woman came in complaining that we’d charged her too much. 有个的老太太进来抱怨说我们收费太昂贵。
Ben rushed to his father, crowing with pleasure. 本欢叫着跑向他爸爸。
He walked along in front of me, holding the lantern. 他提着灯笼走在我前面。
‍Everybody came in the room, singing and smiling. 大家唱着笑着走进教室。