噬脐莫及

Explanation: Umbilical macrophages: nibbled navel. Navel like biting like, out of reach. Metaphor is too late to regret. 　　Usage: Contraction type; as the predicate attribute; containing derogatory 　　Source: Tang Gaoyan Hugh "Don Que command of the history of the country town of Lu-phase state of things": "A missing the machine, no bite and umbilical." Thesaurus:  rude awakening, useless to regret, s too late (to do)