In this January 2020 file photo, a police officer patrols a Beijing railway station with his dog. (YANG YI / CHINA DAILY)

Being pounced on and bitten by an aggressive dog that weighs over 40 kilograms is a nightmare for most people. But it's part of a day's work for police officer Han Siyu.

We must catch bites properly, which requires a lot of practice because it's human instinct to fear dog bites. If a dog feels uncomfortable while biting, it may lose interest in attacking. Then, our training loses its purpose.

 Han Siyu, the Beijing Municipal Public Security Bureau criminal investigation corps canine detachment officer

The 38-year-old Beijing native feels excited when his canine shows such ferocity. It means the animal is one step closer to assisting in the field.

The Beijing Municipal Public Security Bureau criminal investigation corps canine detachment officer has trained police dogs to attack since 2004.

He has been bitten numerous times. But being bitten enables him to test the force and technique of the dogs' attacks.

"I've loved dogs and dreamed of being a police officer since childhood," he said.

"So, I chose to study in the police-dog program when I underwent training in 2001."

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Han started to work in the bureau's canine-training base in Beijing's Daxing district soon after graduating from the police academy.

He raised a dog during his last year at the academy and took the animal to the training base soon after graduating from the academy.

About two months later, his dog experienced hip problems that prevented it from undertaking intensive drills.

It was a huge blow for Han to see his first dog weeded out just when he was about to finish its training.

Han took charge of his second canine in 2004.

The training base imported a batch of pedigreed dogs from Germany that year.

One was kept in a cage for weeks without anyone to train it. Han decided to try. The 1-year-old canine had previously bitten four police officers.

"I prefer to train fierce dogs. Training an overly docile one is boring," he says.

Han said the dog, named Baozi, was pretty hostile about leaving his original trainer.

Han spent about half of his monthly salary of around 900 yuan (US$133) to buy meat, bones and treats. After several months, the animal was amenable to interacting with him.

Then, Han put a muzzle on the animal and took it out of the cage for the next step.

"Training a dog requires a lot of patience and skill. First, I must let it know I won't hurt it. Then, I must make the dog aware that I'm his new trainer and rank above it in the hierarchy," he said.

"It took me about a year to build trust with Baozi through grooming and feeding him. Then, I started to train him to follow my commands."

Police dogs in other programs, such as explosives and drug detection, usually have a fixed master, who trains them from the beginning and takes the dog to do fieldwork. However, dogs in the "attack-and-bite" program need more than one trainer.

There are 30 people working in different sections on Han's team.

Dogs are trained every day from 10 am to 11 am, 3 pm to 4:30 pm and in the early evening. Trainers need to send videos of each session to the team's WeChat group to record and analyze to improve both the trainers' and dogs' skills.

Han said most team members don't take their canines to participate in operations.

People praise the dogs that win prizes or work on cases but typically forget about the trainers.

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Trainers like Han must wear protective clothing that weighs about 10 kilograms. Han said the suits can be hot in winter and sweltering in summer. Trainers limit their time in these clothes to half an hour to prevent heatstroke.

The clothing doesn't fully protect them. Sometimes, dogs' teeth puncture the clothes, leaving a V-shaped line of marks on trainers' skin.

The dogs are encouraged to attack with their full power. But trainers must use restraint, Han said.

"We must catch bites properly, which requires a lot of practice because it's human instinct to fear dog bites. If a dog feels uncomfortable while biting, it may lose interest in attacking. Then, our training loses its purpose," he said.

"Besides, intense confrontations during training may break dogs' teeth, which is their most powerful weapon."

Dogs are also trained to bite certain parts, such as the protective sleeves or pant legs.

But accidents happen.

In this undated 2020 file photo, Han Siyu, the Beijing Municipal Public Security Bureau criminal investigation corps canine detachment officer, and another dog he trains at a base. (PHOTO PROVIDED TO CHINA DAILY)

Some new or overly excited dogs may bite the sleeves first and then quickly attack other body parts, such as hands, legs and torsos.

Trainers with different body sizes and strength levels train one dog so that it can face different criminals.

Nearly everyone on Han's team has suffered waist pain and stiffness caused by the dogs' powerful attacks.

"People undergoing such intensive exercises are prone to injury. Last year, my right leg's ligament was torn during training. I had surgery last February and rested for about four months," Han said.

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Han's family has long worried about his health. They were upset when they saw his injuries in the early years.

So, he hid his wounds from his family and would sleep at the base for several days if he got hurt.

Han's son also loves dogs and has never missed their performances during the base's open-house sessions.

Han's family raised dogs for many years when they lived in Beijing's suburbs.

But their current home downtown doesn't have enough space for a dog, to his son's disappointment.

Still, Han said he hopes to help his boy keep his love of dogs, which he views as something passed down across generations.