In Dehong, a prefecture close to the Myanmar border in Yunnan province, smugglers find many ways to bring drugs into China.

At the Mukang border checkpoint, Zheng Zhaorui and his colleagues check every passing vehicle to prevent the flow of illicit substances, using hard-gained experience and expertise to unmask suspicious characters.

When the vehicle being inspected is a large truck, Zheng has to climb on top of it, inspect its goods carefully and also search under its chassis for any unusual modifications.

"What do you do? Where are you from? What's in your car?" The deputy station chief remains vigilant as he deals with both drivers and passengers.

He uses carefully scripted dialogue and questioning to unmask suspects, examining the smallest change in their expressions and mannerisms. During one check on a bus, something caught Zheng's attention. He checked all of the passengers' ID cards, and after running a background check he discovered that one of them was a recovering drug addict.

The atmosphere grew tense as colleagues came to help and began to carefully check every part of the vehicle. The recovering addict was scheduled for a urine test. "It's easy for people who have used drugs to take drugs again," Zheng said.

After careful inspection, no drugs were found, and the urine test results were normal. The bus was eventually allowed to continue on its way.

In 2017, Zheng uncovered two drug smuggling suspects while inspecting their vehicle. They claimed that they were in the jade business, but the border guard thought there was something odd about their jewelry, which didn't seem to match their story. Eleven kilograms of heroin were eventually found in the car's fuel tank.

Zheng records all his experiences, taking note of such things as the flow of goods into the region, the price of a used car or dialects from different regions.

He is also good at drawing and has sketches of everywhere drugs can be hidden, marking locations for future reference.

In the Mukang checkpoint exhibition hall, Zheng displayed some of the means used by drug smugglers. Women's skin care products, vintage furniture, children's toys and even hollowed-out screws can be used to smuggle drugs.

Finding these kinds of containers is difficult and requires officers to have extensive experience. They also have to learn to follow their instincts, even when that appears to go against common sense, and to be careful. One of Zheng's colleagues was stabbed seven times by a drug dealer while he was inspecting a vehicle. Fortunately, he survived.

In addition to the threat of retaliation from drug dealers, border police working in the hot, humid region are plagued by insects, some of which bite and can even leave a scar. During the 19 years, Zheng has been working at the checkpoint, he has seized more than 500 kg of drugs.