Complex sentence: The most common running gag through both seasons of the series (shown in every first season opening except for the pilot episode) involves the fort's lookout tower: every time the cannon is fired in salute, the lit fuse burns out.
Split into simpler sentences: The most common running gag through both seasons of the series (shown in every first season opening except for the pilot episode) involves the fort's lookout tower. Every time the cannon is fired in salute the lit fuse burns out.