By definition, the articulated leech is two or more flies, joined to make one long, wiggly, artificial. The size in itself is enough to draw attention, but its lifelike swimming motion adds a degree of realism that drives fish nuts. Most often, it's tied in black, but various colors and flashy materials can also be used to create the ultimate attractor.
For increased motion on the triple, you can add weight to the head of the first fly, the tail of the second fly, and the head of the third fly. For a double, add weight to the head of the first, and tail of the second. When you fish them with a strip retrieve, they bend at the joints, and then straighten with a strip, resulting in a swimming leech.