Charcoal rubbing

Charcoal rubbing is an item in the Rocking Out quest. It is obtained by using the plans on 50% Luke together with a charcoal in the inventory. While Luke is distracted, you wrap the plans round his leg and make a rubbing, getting a lovely replica of Rabid Jack's signature.

This will clearly upset 50% Luke, and he'll ask what you are doing with the charcoal and paper, and you'll say that you have "Hydro...endo...cardio...spatula...itis...syndrome."