The Heraldic Significance of Porcupines

On Friday night I dined on High Table at Sidney Sussex.  I was rather intrigued by the ratty looking animal on the right. The Master told me that is was a porcupine, and the arms were those of the college foundress, Francis Sidney.

It appears that the Sidney's adopted Louis XII's emblem after a diplomatic trip to France. And why the porcupine...because it is a formidable enemy (apparently).