What feature does the quill of a feather have that made it useful to write with?

The quill of a feather has a hollow shaft that allows for the storage of ink, along with a pointed tip that can be sharpened to create fine lines for writing. Its flexibility provides control and the ability to produce varying line thicknesses, making it suitable for different writing styles. Additionally, the natural materials of the quill ensure a smooth flow of ink, enhancing the writing experience.