This pen is made from a smeared ferret paw. The overall affect is a textured and rough brush but due to the floating contact points you will get some interesting gaps with varied pen pressure
This can make ferret claw marks as seen in the upper left. As mention in the description the varied pressure creates a very accurate hair strands or string like quality due to the irregular floating contact points made by the finger pads and nails.
This could be used to make grudge like hair, or yarn like string, tangled together.