On this video, posted on YouTube on June 11, 2012, and probably shot around Homs, Syria, a man identified as Qasim Saad Eddine is seen armed with a 50.61 FN FAL (folding-stock).
• a small device that releases a spring or catch and so sets off a mechanism, esp. in order to fire a gun: he pulled the trigger of the shotgun.
• an event or thing that causes something to happen: the trigger for the strike was the closure of a mine.
verb [ trans. ]
• cause (an event or situation) to happen or exist.
• cause (a device) to function.
quick on the trigger
quick to respond.