enigmatic

她的表情很严肃，让人难以捉摸。

Her expression is serious and ___enigmatic.

她脸上带着神秘的微笑，让人捉摸不透。

She had an ___enigmatic smile that was hard to decipher.

她的微笑神秘莫测，从不透露真实想法。

She always has an ___enigmatic smile that never reveals her true thoughts.