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to become frightened; to be frightened (of); to be scared (of)
突然の物音に悸えて心臓がどきどきした。
I was startled by a sudden noise and my heart pounded.
暗い夜道を一人で歩くとき、影に悸えた。
Walking alone on a dark road at night, I was frightened by shadows.
戦争を経験した人々は今も爆発音に悸える。
People who experienced war are still frightened by the sound of explosions.