Answer: their attraction to worldly things.
Both the Prioress and the Monk are presented as religious figures who do not embody the qualities that religious figures are meant to embody. Instead of being pious, modest and frugal, both characters are very fond of worldly things. The prioress is elegantly dressed, and wears a fancy string of beads around her neck. On the other hand, the Monk wears fur and gold jewelry, and he is fond of horses and greyhounds.