The international language of watermelon knocking

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.