China banned the live transport of dogs and cats across provincial boundaries in 2011 without a health certificate signed by a government-approved vet at the animal’s place of origin.

Peter Li, a China policy specialist at the Humane Society International and an associate professor of East Asian politics at the University of Houston-Downtown, said that the mystery pet box phenomenon was not only a “gross inhumanity,” but also a public health risk.

“The fact that China’s surveillance system has failed to capture the illegal trade is because it looks like a normal business operation,” Dr. Li said in an email.

“Those involved in the mystery box ‘business’ are encouraging irresponsible pet ownership, irresponsible consumption habit and encouraging disrespectful behaviors toward nonhuman animals,” he said. “Shipping companies and delivery services have the duty not to handle shipment that is ethically questionable, legally liable and socially toxic.”

He added that while animal-protection groups in mainland China have been encouraging the adoption of rescue animals, the mystery-box model is a supply-driven trade, driven by breeders with too many animals who seek to lure younger customers with the promise of expensive breeds of pets at low prices.

Even among people who have bought mystery boxes of other items, but not pets, there was a recoiling at the idea of mailing animals.

Zhang Luyuan, a 33-year-old staff worker at a tourist attraction in the Chinese city of Fuzhou in Fujian Province, once indulged in blind-box purchases. “Those who buy blind boxes have a bit of wishful thinking and want to get what they want with less money,” he said by phone. But after spending $60 on a mystery box for what he thought were high-quality sport jerseys, he found subpar products inside.

“Since buying that blind box, I learned that meat pies won’t fall from the sky, and I have been buying the products the honest way,” he said, using an idiom similar to “there’s no free lunch.”

He said the delivery of living animals in mystery packages was tantamount to abuse, a lucrative way for breeders perhaps to get rid of those that are ill and unlikely to survive.

ZTO Express, the company behind both botched shipments of animals this month, could not be reached for comment. In a statement on May 4, it apologized for failing to enforce safety laws and said that it needed to “uphold correct life values.”

The company added that it would close the Chengdu delivery facility where the 160 crates were found, would cooperate with the police investigation and would enhance safety training. In another statement on Wednesday, ZTO said it had sought to regulate and reverse the delivery of live animals since May 5. The company added that the animals found in Suzhou were already being returned to their place of origin, but had been stranded at a shipment centers.

The police and postal authorities in Chengdu and Suzhou also could not immediately be reached for comment.

The backlash this month has prompted many breeders to remove their listings from popular e-commerce sites such as Pinduoduo and Taobao.

Li Ruoshui, a 19-year-old university student in Shanghai, said he had bought more than a dozen blind boxes of Harry Potter and anime figurines as gifts over the past two years.

“My sister really enjoys the surprise when opening the box, because you don’t know what you’re going to get,” he said in a phone interview. “I think that’s how blind boxes stand out from other products.”

But he said that the concept of blind boxes should never be extended to living animals, and questioned whether the customers who buy pet boxes actually want to take care of the animals inside or are doing it for the novelty.

“I will never buy pet boxes,” he said. “I like small animals, and transporting them in blind boxes is very unsafe and increases the chances of their abandonment.”

Liu Yi contributed research from Beijing.

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