inscrutable

The Mona Lisa's inscrutable smile has fascinated art critics and historians for centuries.

(Chinese) 蒙娜丽莎那难以捉摸的微笑几个世纪以来一直让艺术评论家和历史学家们着迷。

Behind his thick glasses, the poker player maintained an inscrutable expression throughout the tournament.

(Chinese) 在那副厚眼镜后面，这位扑克选手在整个锦标赛过程中都保持着让人看不透的神情。