It doesn’t seem to make sense that a barbed quill would go in more easily than a smooth one. But Karp and his colleagues discovered that the barbs work just like the bumps on a serrated knife. The knife’s wavy blade concentrates force at the tips of the teeth, requiring less power overall to cut soft foods like tomatoes or bread.
Knife makers have known that for a long time. Now it turns out that North American porcupines know it, too.