kǒu xuè wèi gān
古时订立盟约,要在嘴上涂上牲口的血。指订约不久就毁约。
先秦 左丘明《左传 襄公九年》:“与大国盟,口血未干而背之,可乎?”
口血未干主谓式;作谓语、宾语;指订盟约不久就毁约。
before the blood of the oath is dry (breaking an oath which is just made)