Trout teeth are small, but they can be sharp. And if they happen to cut the material that you’ve wrapped around the hook shank–peacock herl or hackle quills, for instance–the whole thing can come unraveled, rendering the fly useless. One way to keep this from happening is to counterwrap another material, such as wire or hackle, over the top of the body material. The top material crosses the strands of body material, locking them down. This will make your flies last longer, allowing you to spend more time fishing and less time changing flies.