Significant Enemies
The GM can and should declare that an ineffectual foe is not enough of a threat to count as an enemy for effects that grant you a benefit when you do something to an enemy or have an enemy do something to you. For example, the commander ability of the mercenary theme requires you to defeat three distinct groups of significant enemies in a day to recover 1 Resolve Point; a mercenary shouldn’t gain this benefit if all they did was step on three different bugs that had no chance of hurting them. In general, a creature with a CR less than or equal to your character level – 4 is not a significant enemy.
Source
Core Rulebook pg. 242