A gun is fired at Speedy, who runs away. As Speedy is as fast as a bullet though, the bullet cannot catch up to him. Instead Speedy is seen running from the bullet which is keeping pace with Speedy. The bullet is clearly seen, and it is still in its casing. But when a gun is fired, just the bullet flies through the air. But the casing does not fly along with the bullet because it is what contains the propellant, and when fired the casing is left in the gun. This mistake was repeated when a cannon is shot at Speedy. It, too, kept its casing when fired and flew through the air.
The cannon that is shot at Speedy has a rounded back and therefore is a muzzle loading piece (meaning that it is loaded from the front). But a muzzle loader does not fire fixed ammunition which uses casings. Instead the propellant is loaded first, then the projectile, all separately. Only breach loading artillery uses fixed ammunition, and as with a firearm, the projectile is the only thing that is fired and travels through the air (while the casing is left in the cannon).