The shop owner - named only as Zhang - has since admitted to police that he bought 2kg (4.4lb) of poppy buds - which contain the plant's seeds - for $100 (£60) last month, crushed them into a powder and started to add that to his noodles, the Hua Shang Bao daily reports . Police said the unprocessed seeds contain enough opiates to gradually build up in the body and eventually trigger a positive drugs test result. According to the South China Morning Post , poppy seeds used to be a popular ingredient in Chinese hot pot sauce until their use was banned.