Wall Turret

Wall Turrets, also known simply as Cannons are dangerous traps that appear in a couple of locations in. They are connected to the walls of certain rooms; the room containing the Big Key in the ALttP:, and a room in the third floor of Ganon's Tower known as the Corridor of Cannons. They move along the wall in a predictable back-and-forth motion, firing cannonballs at regular intervals. They are placed on either side of the room, so the cannonballs will assault Link from both directions, making it hard to pass. Link has to time his movements carefully to get beyond these traps, as they cannot be destroyed.

The firing motion of Wall Turrets is quite exaggerated, like a large mouth spitting outwards, implying that these traps may in fact be magical or living in some fashion, rather than purely mechanical.

Trivia

 * The amount of cannonballs fired by Wall Turrets depends on how many other enemies are active nearby; even in adjacent rooms. For example, if the enemies to in the rooms to the west of the Wall Turrets in the Desert Palace are still alive, the cannonballs will only fire a total of four cannonballs at a time. Despite this, they will still go through the action of firing even when they do not launch a cannonball.