Are they what make porcupines vertebrates? (6)
I believe the answer is:
spines
But I can't explain it at all! Could you help me understand?
(Other definitions for spines that I've seen before include "Sets of vertebrae" , "Thorns or backbones" , "Porcupine quills" , "Snipes at backbones" , "Quills; prickles" .)