expression, noun
shrewd face; knowing look
Rare expression describing a facial expression that suggests cunning, worldliness, or inside knowledge. Often implies someone who is not easily fooled.
彼は抜からぬ顔で、こちらの手の内を見透かしているようだった。
With a shrewd look, he seemed to see right through our plan.
抜け目ない is a common adjective meaning 'shrewd' or 'sharp', while 抜からぬ顔 is a rare noun phrase specifically describing a facial expression.
The phrase combines the negative form of the verb 抜かる (to be careless) with 顔 (face), literally 'a face that does not slip up', suggesting a vigilant or cunning expression. The exact origin is uncertain.