As follows:

The black flotsam in the flesh of the mussel is removed, that is fecal matter.

The black part in the mussels can be eaten, just get rid of the dirt that connects the outside of the shell to the inside, the black part is the gut and other internal organs, it's okay to eat it, but you can clean it off. And the sand must be cleaned off, soaking soft is very easy to clean.

Expanded:

Precautions:

Can not be eaten with cold foods: Tempeh is cold in nature, it is best to avoid eating with some cold food *** with food, such as cabbage, cucumber and other vegetables, you should not drink some immediately after the meal, such as soda, ice water, ice-cream such as ice cream, and pay attention to eat or not eat! Watermelon, pears and other cold fruits, so as not to cause discomfort.

Baidu Encyclopedia - Mussels