Audio problem: In the opening heist sequence a clown grabs a bald bank teller and the teller says "Please no, no!" while being thrown over the counter, however, his voice doesn't match his facial expression. His voice is loud and terrified in fear and yet his lips and face expression barely react. (00:02:55)
Audio problem: In the scene where Alfred is stitching up Bruce, Bruce says "I wanted to inspire people." As he says "people" the shot changes and his lips aren't moving, but the audio track continues.
Answer: The gun fires using compressed carbon dioxide as a propellant. The cable is wrapped in a coil around a motorized turbine within the gun. The pulley system in Batman's belt buckle allows him to reel himself in hands-free and still maintain equilibrium. There is a four-pronged grapple at the end of the cable. This is what is magnetized, creating an attraction between it and the monofilament cable. This ensures that the grapple will attach itself to the cable for a secure hold. This is why the magnet itself does not need to be especially strong to support any amount of weight. It also explains the relative ease with which it can be detached and its seemingly "magical" ability to wrap itself around various objects.
Phixius ★