在奈何桥卖孟婆汤
[zài nài hé qiáo mài mèng pó tāng]
This idiom comes from Chinese folklore. 'Naihe Bridge' is in purgatory, and 'Mengpo's Soup' is given before souls reincarnate so they forget their past lives. The name humorously imagines operating a stall selling this soul-fogging soup to travelers in limbo between life and afterlife.