Zhang, 27, is among an estimated 3 million "waimai xiaoge" - food-delivery lads or boys - who buzz through China's streets every day on scooters. They dodge pedestrians. They thread through traffic. One-way signs? They are for others.
And many have the scars, scrapes, scabs - or worse - as evidence of the risks.
Comprehensive official data is unavailable, but police in Shanghai say a delivery boy is seriously injured once every 60 hours on average. In Shenzhen, just north of Hong Kong, the food delivery boys account for 12% of traffic crashes. In Nanjing, northeast of Shanghai, about three delivery boys are injured every day on average.
In the past 18 months, local media in the country chronicled 13 deaths and published 125 accounts of serious crashes. The news reports offer a tiny - but telling - glimpse into the chaos: stories of riders who die in late-night hit-and-runs, of head-on collisions into trucks, of electrocutions during rainstorms.
"My wife begs me to do something different, less dangerous," Zhang said, grinning. "But the money is good."
That's because China is becoming a delivery nation.
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Some 400 million people use smartphones to order piping hot meals to their doorstep - up to several times a day.
It's part of a lifestyle revolution in China as its growing middle class reshapes the country, a high-tech network made possible by low-tech, low-cost labor.
It's also a system of frenetic workloads during meal hours and through bad weather, of unforgiving dispatch algorithms and unruly traffic, close calls and sometimes fatal crashes.
And at a time when governments worldwide are grappling with the regulations - and implications - of delivery apps such as Uber Eats or Deliveroo, China's $36 billion food-delivery industry offers a vision of the gig economy taken to a chaotic extreme. Even authorities are taking notice of the grueling and dangerous conditions.
"It's necessary to fundamentally change the takeout platforms' logic of [valuing] 'speed only' for 'profit only,' " the ruling Communist Party's official mouthpiece, the People's Daily, said in a 2017 editorial. "Can these platforms have more humane algorithms and let the delivery boys have more time on the road? Can users be more empathetic and understanding?"
Perched outside a shopping street frequented by Russian traders, Zhang acknowledged the dangers that come with his job. But it was a decent living for a seventh-grade dropout from the countryside outside Handan - a bleak central China steel town perhaps best known for coming in dead last in nationwide air-quality rankings.
Zhang works 14 hours a day, six days a week, running orders for the giant company Meituan-Dianping. Zhang says he averages about $1.10 per delivery and $1,000 a month. If he works extra hours, particularly during freezing winter months, Zhang can haul in $1,500 a month, more than what some software coders can make.
As soon as Zhang turns on the Meituan app around 7 a.m., the automated dispatch system starts flashing jobs on his screen based on his position, chiming: "You have unconfirmed deliveries. Please respond as soon as possible."
The pressure to accept multiple orders is high, Zhang said, because riders who decline jobs are punished by Meituan's algorithm. The highest-earning riders, called "Happy Runners," must accept 99% of orders they're assigned.
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As orders peak that day about 11:20 a.m. - white-collar workers in Beijing typically sit in large groups for lunch at noon, sharp - Zhang is often juggling more than 10 orders at the same time, ferrying in his scooter's insulated box a smorgasbord of Shanxi noodles, Starbucks lattes, dumplings and dim sum.
Zhang coolly plunges along streets against the flow of traffic, blows through intersections, ducks into high-rises and sprints up stairwells to drop off meals with minutes, sometimes seconds, of his allotted time left to spare.
The time crunch is made worse because the software doesn't calculate road closures and traffic controls that crop up overnight. Yet riders get penalized for late deliveries, and if a customer files a complaint on Meituan's app, they could be fined their entire day's earnings or booted off the platform altogether.
"Know your terrain, constantly calculate in your brain, and move with precision," Zhang said.
Since he started working at 15, he's sewn jackets, welded steel on construction sites and assembled basketball backboards on a Guangdong factory line.
"But that was all physical energy," he said. "Delivery exhausts your mental energy. There is nothing quite as stressful."
As accidents involving delivery riders became widespread in recent years, the two large food-ordering platforms that dominate the Chinese market - Meituan and Eleme - have tweaked their dispatch algorithms to be less demanding, riders said. On rainy days, for instance, they can be late a few minutes without penalty.
Chinese police say reckless delivery boys are also to blame and have proposed measures such as installing tracking chips to punish bad driving.
One of Zhang's Meituan co-workers, who spoke on the condition that he be identified only by his surname, Li, said he rides against the flow of traffic and blows through red lights on a near-daily basis. Police fine him often but do not pose much of a deterrent: Most traffic tickets are paid off for about $3.
"Who wants to run red lights and break traffic rules if the time pressure isn't so hard?" Li said. "I do it because otherwise the customer would file a complaint, and I'd be banned from delivering."
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A Meituan spokeswoman said the company requires mandatory road-safety training at the time of hire for its 2.7 million delivery workers and regularly offers refresher courses. The company declined to comment further.
In the past two years, delivery drivers in a handful of cities, including Shanghai, have managed to form unions and campaign for better labor conditions - moves that required a level of tacit support from the Chinese government.
Labor researchers say authorities should be more proactive.
Cheng Xusen, chair of the e-business department at the University of International Business and Economics in Beijing, said Meituan and Eleme outsource delivery to hundreds of small companies with different levels of training and job protections. Most drivers work without contracts, leading to problems such as inadequate injury compensation.
"It's the regulator's job to close that loophole," Cheng said. "At the end of the day, the government needs to do more to ensure workers' legal rights."
But for many workers such as Zhang who have held other menial jobs across China, delivering food in the big city still appeals with its good pay and sense of freedom.
Zhang can take off every Sunday to do laundry and relax in the 50-square-foot room he shares in far east Beijing with a delivery boy who brought him into the business four years ago.
During midafternoon down times, he's glued to his phone chatting with his friend Chen, a co-worker who crashed into a guardrail and tore a knee ligament while rushing a lunch delivery this summer. Chen has been recovering at home in Inner Mongolia on a diet of porridge and dried dates - he's eager to get straight back to work.
On most weeks, Zhang calls home to his wife and two sons three or four times. After he fell off his scooter in August, Zhang took the 4 1/2-hour bus ride back to his village, where his young family lives in the two-bedroom apartment he bought for about $27,000 with his earnings.
As Zhang rested his leg, his wife asked whether he might finally decide to find a different job.
He gave the answer he gives every year, he said: "Maybe next year."