Knit the brows and a stratagem comes to mind.

眉头一皱，计上心来。

《新英汉大辞典》

It did all our hearts good to see him spit in his hand, knit his brows, and make the blade sing through the air.

我们所有的人看到他往手上啐了口唾沫，拧紧眉毛，将弯刀舞得呼呼生风的样子都大为高兴。

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