If we look under a microscope a woolen thread, we can observe that it is covered with scales like a pine cone, overlapping one another and always directed towards the tip of the fiber. So, if the wire is cut, inside there is formed by a bark called the cuticle, which is inserted in a channel that is empty or that most often contains a substance called bone marrow. A wool thread 10 cm long, stretched slowly, it will become 13 cm long.

 

Pellets come up  because it’s  used a little wire twisted to produce a product with all the softness of wool. Grinding heads shed small pieces of hairs that form the pellets.
Should therefore not rub too much of them, especially  covers are not to be beaten or rubbed.
To remove them you must use a special comb  available at stores of appliances.