You cannot fail to have heard the jeering from the Chinese fans against the Japanese players at the Asian Cup in Chongqing.
Against Thailand on Saturday night it was particularly vociferous, almost drowning out the sound of the national anthem before the game.
Whenever Thailand attacked, which wasn't often, the crowd went wild.
When Japan had possession, the crowd booed, willing a mistake.
All in all, though, this is good experience for the Japanese players, if not a particularly pleasant one.
The J.League is played in a very friendly environment, and the players rarely face any hostilty from the spectators, so this will help build character.
This is not the first time I have seen the Chinese fans behaving badly.
Shortly after I left England to work in Hong Kong in 1989, Verdy (then known as Yomiuri) went to Hong Kong to play the South China Athletic Association in an Asian Club Championship match.
The national stadium, which held only 28,000 before it was redeveloped, was packed, and the fans showed no mercy on the Japanese players, hurling abuse, as well as plastic bottles and other debris, at the bench.
I have also seen Chinese turn on Chinese, when I went to report on South China again, this time against Dalian in Liaoning province.
Although South China lost 1-0 on the night, they won through over the two legs.
The Dalian supporters were not happy with their rich, spoilt, southern cousins with the dyed brown hair and pop-star looks.
First they set fire to the stadium, with small fires burning rubbish all over the place after the final whistle, and then they pelted the minibuses taking the Hong Kong players back to the hotel.
In Hong Kong, the press were allowed to travel with the team, and I kept my head down as the missiles hit the windows. There were lines of police, but they did nothing to stop it.
The boss of the South China team had promised to take the players, and me, as his English guest, to a casino to celebrate the victory.
After returning to our seaside hotel, though, we were advised to stay in, as it would not be safe to be seen in town, with angry Dalian fans still roaming around.
So, when people refer to football hooliganism as "the English disease," I always call it "the Chinese disease."
The Japanese players are discovering this now.