don't look a gift horse in the mouth
口语·劝人不要挑剔收到的礼物
例句
He gave you an old watch, but it's free—don't look a gift horse in the mouth.
典故来源
源自古代马匹交易，通过看马的牙齿判断年龄，但若马是礼物，挑剔年龄被视为忘恩负义，该谚语可追溯至16世纪。