This humorous and very painful image of a pit bull picking a fight with the wrong animal -- a porcupine with very long and sharp quills embedded mainly in his face -- is visual evidence of a worst-case scenario that can be avoided very easily with a strong leash.
Porcupine needles aren't generally a life-threatening problem, but you can avoid an expensive and needless trip to the vet by keeping your curious pet out of harm's way.