to beat the breast
擗 centers on a physical gesture of grief or distress: beating one's breast with the hands.
擗 combines 扌 (hand) with 辟, which likely contributes the sound and may relate to striking or separating. The exact historical development is uncertain.
The hand radical 扌 beside 辟 suggests using the hands to strike one's own chest in a gesture of mourning.
For ヘキ, imagine someone beating their breast and making a hacking cough sound: hack -> ヘキ, as they strike their chest in grief.
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