MacGyver employs his resourcefulness and his knowledge of chemistry, physics, technology, and outdoorsmanship to resolve what are often life-or-death crises. He creates inventions from simple items to solve these problems. These inventions became synonymous with the character and were called MacGyverisms by fans. MacGyver was unlike secret agents in other television series and films because, instead of relying on high-tech weapons and tools, he carried only a Swiss Army knife and duct tape but never a gun. One episode shows the reason being that a boyhood friend of his was accidentally killed by a revolver he was not supposed to have. One other episode shows him only using a captured gun by taking it apart to use as a kind of wrench, with the trigger guard doing the job of shutting down a valve tap. In the opening gambit of the pilot episode, MacGyver is briefly seen shooting an AK-47 at a group of enemy soldiers before passing the gun off to the man he was rescuing. This is the only time MacGyver fired a weapon during the series.