How Do You Know They’re Pests?

On top of a dusty stone pillar, a raven-haired, purple-eyed lady stood, watching two figures below. In the last human city, they carved glowing magic circles into the parched earth, their movements precise and synchronized.

"How did they figure it out?" she wondered, a glimmer of astonishment in her otherwise calm expression.

The two's faces were filled with panic as they engraved the magic circles. It did not go unnoticed by the lady perched on the pillar. Maxim engraved the last line of the circle on the ground, finishing which caused it to glow brightly. 

Within the circle, footsteps appeared out, and this time, they could see someone's foot along with the steps. 

From the footwear this person wore, which were a pair of straw sandals, the two men figured out it was a woman. This one clue had significantly narrowed down a lot of suspects.