According to your description, the dense white lines in the black belly of the seeds you bought may be parasites. In this case, here are some suggestions:

1. Prevention of infection: Pay attention to food hygiene, avoid eating unclean and cold food, wash your hands frequently and pay attention to personal hygiene.

2. Heat and cook: Before eating black seeds, be sure to heat and cook them to kill parasites and eggs. Boiled black seeds can be safely eaten.

3. medication: if you have been infected with parasites, you can take medication under the guidance of a doctor. For example, Changchongqing tablets can be used to treat parasitic infections.

4. Avoid raw food: Raw or uncooked seeds are easy to be infected with parasites, so it is best to avoid raw or uncooked seeds.

In short, in order to protect your health, please follow the above suggestions and pay attention to food safety and personal hygiene. If the problem persists or other symptoms appear, please seek medical advice promptly.