The practice of knocking on watermelons to determine their ripeness can be found across cultures. In China, it is considered an endearing national habit.
Savvy buyers tap on the fruit before buying, to ensure their money is well-spent. The perfect fruit should neither be underripe nor overripe.
Some buyers knock on the fruit despite not knowing what the hollow sound means just to negotiate a better deal from the seller.
As fruit sales have moved to online platforms in a big way, those who make a living by checking the quality of the fruits with their knuckles are much in demand.
Lee is one among a growing group of watermelon knockers who work with farmers in Panggezhuang, a sprawling production base in Beijing's southern Daxing district.
Their task is to conduct knock tests on behalf of e-buyers and ensure that the fruits selected to be sold online are uniform in size and quality.
Lee, who was once an award-winning car racer, now describes himself as a "goalkeeper for watermelons". He quit car racing about four years ago due to disruptions caused by the COVID-19 pandemic.
He learned about melon-knocking as an emerging profession through a friend and decided to become an apprentice in Panggezhuang, where he was tutored by an experienced farmer. After a year's trial and error, Lee worked independently as a quality checker.
"It is a highly empirical task. During the apprenticeship, I often cracked open melons to confirm my judgment. There are just no shortcuts," he said.