* In the last part of the film, Vincent criticizes Max for being trapped by the routine of his life and being unable to adapt or change for the better. But in the final confrontation and Vincent's gun runs out of ammunition, his hand reflexively goes to his belt to retrieve a fresh magazine only to find out that he doesn't have any left. So in a way, Vincent too is trapped by routine.
** Made even more interesting that in the exact same shootout, Vincent fails to kill Max because of his routined reflex of performing a chest-chest-head tap. He attempts to shoot Max through the subway door, but ends up hitting the steel beam located between the two windows (perfectly in the middle, by the way). Max empties his entire magazine without aiming properly, including through both windows - and actually hits his target mortally. The roles of the two leads are thus perfectly reversed by the end of the film.
* Getting shot in the ear does in fact result in losing the balance more often and finding it harder to concentrate - at best. Exemplified by Vincent getting subtly clumsier after suffering such a wound (tripping over a chair he himself threw through a window, getting stuck between two closing subway doors, taking longer to react and make choices, etc).
* A previous case involving a cab driver who apparently "went crazy" shooting several people in a single night, then killed himself, is implied to show Vincent's intentions re Max. But since all the hits are related to the same case, it's unlikely the police would believe these deaths were the result of Max going crazy.
** Vincent's plan doesn't necessarily involve making the police think Max went crazy, but rather confusing the issue so that he can get away. It's enough if the police think Max did it. If they realize it's a contract killing, Vincent doesn't care. He only cares that ''he'' doesn't get caught.