When visiting Japan, you should follow a couple of set rules when using chopsticks.
Also, do not shovel the food rapidly into your mouth using your chopsticks and never chew on your chopsticks.
Note that two people eating from the same dish at the same time is also considered impolite as is rummaging a dish for only the things you like to eat.
For example, the chopsticks must never stand upright in your rice bowl as this is the way a bowl is offered to the spirit of a dead person.
Japanese food culture consists of sharing meals rather than having individual meals for everyone.
SOURCE: tg . tripadvisor . jp/news/graphic/chopsticksmanners/
