The bobber KHB was refering to is an indicator"flyfisherman dont call them bobbers but that is exactly what they are." the idea is to be able to detect a strike and also allowing a nice dead drift in most cases very near the bottom where most of the food is most of the time.A general rule of thumb for how far from the fly to attach the indicator is about one and a half times the depth of the water you are fishing.For instance if the water is 3 ft deep then the indicator should be placed about 5 ft from the fly.These indicators come in a variety of shapes sizes colors and designs.Different strokes for different folks.Some people frown on they're use citing it's too much like bait fishing and makes fly fishing a little to easy,again different strokes.I personally do use them quite a bit unless I'm fishing close cast range pocket water and or very deep water , streamers and of coarse dry fly,emerger fishing.