Rewinding time a few moments before the bright yellow fireball exploded. The group of level 18 deer was minding their own business, eating the fruits and berries that were available around the area.
With the three kobolds being extra careful in their plan and with their knowledge of the deer, the twins were able to keep a safe distance between them and the group of deer to prevent themselves from being noticed. While Ethan was also able to keep his spell casting as silent and as unnoticeable as possible even keeping the heat that the fireball emitted from spilling outward. He succeeded in making the group of deer totally didn't realize that they were being targeted.
But the moment Ethan released the bright yellow fireball from his control and threw it past the thick bush, towards the deer, the group of deer had instantly noticed it.