This was another thing about Zillah that irritated Tod. She was so plumb ignorant of magework. It was almost as if she refused to learn on purpose, and possibly encouraged Marcus to make a noise so that she could leave. He allowed that this was partly due to the lack of confidence - someone, way back in Zillah's history, has evidently sapped her confidence pretty badly - but he also suspected that it was due to arrogance. In some secret place in her mind, Zillah felt that she has no need to learn.

A Sudden Wild Magic ~ Diana Wynne Jones