China poison dumpling in Japan

Until today, it seems like they haven't find out the root cause to the poison dumpling in Japan.

So far, the speculations are

1. Deliberate poisoning
Although it is possible, but I don't think people are so silly to damage the reputation. Except those who has other agenda.

2. Loose control in the factory
Maybe this is the cause, but generally factory for export should have stringent quality control standard.

The funny thing is nobody seems able to give a firm answer to the root cause.

The consequence is the damaged relationship between two countries. The food safety standard in China also raised as questions.