Threatening behavior by predators causes a porcupine to extend its quills, and porcupines only inflate and extend their spines as a defense mechanism. Given these facts, porcupine can use its quills as a what among the following options:
- encoded information
 - threatened
 - defense mechanism
 - cushion
 - protective bony armor
 - cleaning mechanism
 - if humans disturb bears
 - brush


 

   defense mechanism      