Why does beef offal have a texture like long black hair?

Taenia saginata may be dyed black by blood.

It may be that Taenia solium is dyed black by blood, and Taenia solium stays in the intestine, which will not cause much damage, but it often causes weight loss, occasional abdominal pain, loss of appetite and itching around the anus. Parasites are pathogenic lower eukaryotes, which can be used as pathogens or carriers of diseases. Parasites are characterized by all living things in or attached to the host for nutrition or shelter for their survival, development or reproduction.