The term 'HEDGEHOG's Spine' is a reference to the quills of a HEDGEHOG, which are made up of stiff hairs that are sharp and pointy. The crossword solution for this term is 'QUILL, ' which is a five-letter word meaning a feather or a stiff hair. Quills are typically found on porcupines, hedgehogs, and other animals with spiny fur. Hedgehogs use their quills as a defense mechanism against predators, and they can be raised or lowered depending on the situation.