Left: A microscopic image compares the size of a North American porcupine’s quill tip with the tip of a narrow, 18-gauge needle. Right: In a live porcupine, the partially hidden quills usually lay flat along the herbivore’s body, amidst other hairs, until and unless called into action.

Left: A microscopic image compares the size of a North American porcupine’s quill tip with the tip of a narrow, 18-gauge needle. Right: In a live porcupine, the partially hidden quills usually lay flat along the herbivore’s body, amidst other hairs, until and unless called into action.