The humble watermelon. The epitome of summer. But how do you know if it's perfectly ripe? Well, one theory is that if you knock hard on the outside, the sound you hear will help determine if it's ready to eat.
That theory lead to a huge online debate in China about what kind of people engaged in the art of 'watermelon knocking'?
The discussion, which thousands of people contributed to on the Chinese micro blogging site Sina Weibo, was kicked off by an obscure event thousands of miles away in Italy.
It all began when a Chinese social media user posted the picture below of a sign in an Italian supermarket asking customers not to knock on the watermelons. The sign was stuck in a crate full of watermelons which read: "please stop knocking on the watermelons, they will not respond to it!"
There is no indication that the supermarket was targeting this message at customers with Chinese heritage. The sign was in Italian not Mandarin. But somehow it was taken as an attack on a practice which some Chinese observers regarded as being unique to their national customs.
According to What's On Weibo, the photo was widely shared after Chinese media outlets reported that the notice was aimed directly at Chinese customers.
But some social media users were quick to establish that the art of knocking watermelons is not exclusive to China and is in fact universal. The viral photo was originally posted by a user on Weibo who calls himself 'Isolated Guardian'. He is allegedly a Chinese man living in Milan. The photo has since been removed from his page.
Many shared jokes aimed at the supermarket sign.
Some people shared photos of themselves listening for a response from watermelons.
Others pointed out that the concept of watermelon knocking has been passed down from their parents.
A quick online search will reveal that Chinese social media users are not alone in their thinking. Watermelon knocking and listening for a hollow sound is indeed a near universal concept. A vast array of videos and blogs provide with advice on how to pick a good watermelon. It even appears in film and animation. Popular Russian cartoon, 'Nu, pogodi!' included watermelon knocking as part of an episode.
One video comically claimed to have a magic formula but the end result was not very convincing. There's even a smart phone app designed by Chinese university students to you help you in your endeavour to find the ideal watermelon.
There are no absolute guarantees about what to do when it comes to choosing fruit. But at the risk of causing an international diplomatic incident we would suggest there some common ground about what to look for to choose the perfect watermelon.
►Feel the weight of the melon. The heavier the better.
►Press on the watermelon. It should feel firm and if it springs back, it's ready to eat.
►Look at the markings on the melon. A yellow patch on one end indicates it's ready.
Of course if that all that fails, you could always, knock and wait for a reply.
来源：中国日报网双语新闻 英文来源：BBC 编译：yaning