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to knit (one's eyebrows); to furrow; to contract
「顰める」 has another reading with different meanings.
彼は眉を顰めた。
He knitted his eyebrows.
なぜそんなに眉を顰めるのか。
Why do you knit your eyebrows so much?
彼女は心配そうに眉を顰めていた。
She was knitting her eyebrows worriedly.