臍を噛む

定義

1. to bite one's own navel
2. to worry about something that hasn't happened yet; to deeply regret something that has already happened
   idiomatic

例文

“なほ宥し沙汰有らんと欲するの処、今自殺し畢んぬ。後悔臍を食むも益無し”

They wanted to be forgiven and for the matter to be resolved, and now they've committed suicide and things are finished. There's no sense regretting it and chewing on your nails.

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