Rat meat is passing for mutton in China these days.

Police have discovered a ring of criminals who were using spices to flavor rat, mink, and fox meat at marketplaces. So far, 904 people have been arrested, and nearly 20,000 tons of tainted or fake meat has been confiscated.

The arrests came after a sharp crackdown in food safety measures in Shanghai and Jiangsu after sudden outbreaks of bird flu, which is a major problem in China right now. Health officials there recently updated the death toll from H7N9–a new and particularly virulent strain of the disease–to 27, the latest victim a 55-year old man. 26 people have recovered from the virus. Scientists have confirmed that the flu is being passed to humans from chickens.

Food safety is a growing concern in China, as is the safety of the drinking water. More than 16,000 rotting pigs were reportedly found in a main water source in Shanghi in March; officials believe overcrowding of a nearby pig farm was to blame.

“Food safety crimes are still prominent, and new situations are emerging with new characteristics,” the Ministry said in a statement.