Continuity mistake: When Vilain has the gun to Billy's head he has it in his right hand. However when he is squeezing the trigger, it's his left finger. (00:36:00)
Suggested correction: It seems to me that it's still his right hand but the camera angle changed for the close up for a better reveal of the trigger pull. So in real life, the camera would have been to JCVD's right side during the scene, but then the camera switches to his left side for the close up. Watching it in real time, it can look like the camera just does a zoom in and now the hand has switched.