* a weapon may only be used by a worm if that worm is standing on a box containing a picture of that weapon.
* the worm may fire the weapon if it is touching the box, even if it not standing on top of it.
* the worm may fire the weapon if it is adjacent to another worm which itself is touching or standing on a picture of that weapon (and similar for any number of worms in a chain).
* the worm may fire a weapon mid-jump provided it was last touching or standing on the box when it left the ground.