There are breaches of etiquette – drenching your rice in soy sauce, for one – and then there are heinous acts of “sushi terrorism”.
Japan’s signature cuisine is at the centre of a police investigation after customers at revolving sushi restaurants posted video clips of themselves interfering with food and playing pranks on other customers.
The incidents have sent shares plummeting in a leading kaitenzushi chain and prompted operators to rethink how they serve their dishes.
Several acts of what is being called “sushi terrorism” have emerged on Twitter and other social media in recent days, although some apparently date back weeks, and even years.
A clip of the most egregious culinary crime, which has been viewed almost 40m times on Twitter, shows what appears to be a teenager licking the open top of a communal soy sauce bottle and the entire rim of a teacup, which he then places back on a shelf.
If that wasn’t bad enough, the 48-second clip shows him licking his finger and using it to touch two pieces of sushi, presumably ordered by another customer, as they travel past on the conveyer belt.
The video, filmed at a branch of the Sushiro chain in the central city of Gifu, prompted stocks in the restaurant’s parent company to plunge nearly 5% on Tuesday.
Other videos show people at other chains putting wasabi on passing pieces of sushi and licking the spoon from a container of green-tea powder that is used by multiple diners.
While the small number of incidents hardly points to a sushi crime wave, the videos have sparked uproar in Japan, where the industry is worth an estimated ¥740bn (£4.7bn/$5.7bn).
Most of the outrage is reserved for those who show contempt for the country’s high standards of hygiene.
“This is sickening,” one Twitter user wrote, with another adding: “I can’t go to conveyor belt sushi restaurants any more.”
Sushiro, the market leader, said this week that the man who made the viral video had apologised, along with his parents, but added that it had filed criminal and civil cases.
The clips prompted Sushiro to replace all of the restaurant’s soy sauce bottles and rewash its teacups. It has also stopped placing condiments and utensils on each table at the restaurant in question and others located nearby, and is asking diners to collect them from a serving point, Japanese media reports say.
Two other chains, Hama Sushi and Kura Sushi, have also said they plan to take legal action, with the latter planning to install cameras above conveyor belts to monitor customers, Jiji press agency reported.
While some social media users spoke of their nausea after watching the clips, others voiced sympathy for kaitenzushi operators.
“I’ve always wanted to go to Sushiro but haven’t been able to because it’s always crowded,” the singer Yuya Tegoshi tweeted. “But the situation now is the absolute worst for them, so I’m definitely going to visit.”
The firm’s president, Kohei Nii, said he had been overwhelmed by the outpouring of support, tweeting: “I’m so grateful I could cry.”