Zombie Cliché Lookout:
Guns do funny things in movies. They can shoot hundreds of rounds without reloading in one scene, then inexplicably run out of ammo in the next. When the plot calls for it, they can jam, misfire, be loaded with blanks, and have the safety on. Depending on the character using the gun, they can be super accurate with no recoil, or completely unmanageable.
One of the most interesting gun tricks is the way their sound effects change based on how important that shot is. Generally a small handgun makes a popping sound when fired, but if it’s shot at the last second to save a hero’s life, it’s the loudest damn gun in the world. Guns are funny that way.