The same traits that allow barbed cactus spines to readily penetrate animal flesh also make the spines more difficult to dislodge, a new study finds. The microscopic barbs on the spines are layered like shingles and sized perfectly to snag muscle and collagen fibers. When testing the anchoring power of various spines, the researchers discovered that a single cholla spine could hoist a half-pound hank of pork shoulder.