Final answer:
One unusual aspect of relief in Egyptian art is the depiction of lower-class women in a more lively and informal manner, with their faces shown frontally and depicted in a sinuous manner.
Step-by-step explanation:
In Egyptian art, one aspect of relief that is not unusual is the convention of showing the main figures with the head in profile, shoulders facing forward, and legs and feet in profile. This convention is used both in painting and relief sculptures. Additionally, the use of sunken relief technique and the depiction of figures adhering to a standard set of proportions are also common features in Egyptian art. However, one unusual aspect is the depiction of lower-class women in a more lively and informal manner, with their faces shown frontally and depicted in a sinuous manner.