那一抹埋在心里的苦笑
[nèi yī mŏ mái zài xīn lĭ de kŭ xiào]
That trace of wry smile buried in the heart. It is quite artistic in its way, evoking images of deep emotions inside oneself, likely tied with personal stories, bittersweet experiences, or complex emotional moments that are not easy to convey to the general public.