Porcupines sport some 30,000 quills, which easily penetrate flesh--and then stay stuck in it. Now, scientists have analyzed the shape of individual quills to discover what makes them so effective--and how we can harness their power for medical devices. The study is in the Proceedings of the National Academy of Sciences . [Woo Kyung Cho et al, Microstructured barbs on the North American porcupine quill enable easy tissue penetration and difficult removal ]