The violin: How much do you need to draw? What can you omit?
How different can you describe it from the actual subject? How innovative can you be in your mark-making?
How can you make sure that people not only recognise what it is but also know that it is you that drew it?
How do you put your mark on something?
How can you keep the eye interested? How suggestive can you be? How much do you rely on the viewer to fill in the details?
How simple or spontaneous can something seem yet is so difficult to accomplish.