This seems to be the most difficult maneuver in tatting. If you are tatting right-handed, once you pass the shuttle over or under the working thread and while the loop is still loose, relax the left hand fingers just enough to loosen the tension on the thread. At the same time, pull the shuttle thread tight with the right hand. If done quickly enough, you will feel a pop as the loop flips from the shuttle thread to the working thread. If you are using two different colors, say red on the ball (working) thread and blue on the shuttle, you will see the loop change from blue to red.