 FAKE: SPOILERS: Near the end of the film when Cain jumps through the  window to fight Luke, they both fall to the ground. As Luke gets up,  he throws his gun away, then begins to chase after it as Cain  tackles him to the ground once again. It appears the original idea  was for Luke to drop the gun when hit by Cain, but the actor missed  the cue, and had to throw it away (quite obviously) instead. They  probably couldnt do a retake as they had destroyed the one window  they had for the shot.