@miez: Perhaps you are right, and I should not have gotten so angry. Now that I know you're using the pistol, I can clarify for you what's going on: it is sometimes difficult to hit things with the pistol, but that is just the nature of the gun. It performs polygon collision detection to detect hits and the worms, which are rather small, can be difficult to hit sometimes with a slow projectile weapon. So I say again: they are not invincible. You just have to aim a little better. The collision hull on the fist is actually smaller than the fist model to ensure that you do not miss your target by hitting the floor/wall next to it.