Threatening behavior by predators causes a porcupine to extend its quills, and aggression is active, harmful and offensive, threatens all and benefits none. Given these facts, what by predators cause porcupines to extend their quills among the following options:
- hypothyroidism
 - killing insects
 - kisses
 - aggression
 - love
 - hyperthyroidism
 - kinetic energy
 - cohabitating


 

    aggression     