question:  Why does Shannon reach for his gun when Beamish introduces himself?
context: The Blue Behemoth By LEIGH BRACKETT Shannon's Imperial Circus was a jinxed space-carny leased for a mysterious tour of the inner worlds. It made a one-night pitch on a Venusian swamp-town—to find that death stalked it from the jungle in a tiny ball of flame. With Shannon's Imperial Circus, the Greatest Show in Space, plastered so thick with attachments...." I've wet-nursed Shannon's Imperial Circus around the Triangle for eleven years, and I know. Nobody insults Buckhalter Shannon's Imperial Circus to Buckhalter Shannon's face unless he's tired and wants a long rest in a comfy fracture-frame. I had plenty of time to think how I only weigh one-thirty-seven to Shannon's one-seventy-five, and how I'm not as young as I used to be. The little guy looked at Shannon with pale blue eyes like a baby, and his voice was softer than Bucky's. Bucky Shannon sighed, and let his fist start traveling, a long, deceptive arc. It was the most complete dead-pan I ever met, and you couldn't see into those innocent blue eyes any more than you could see through sheet metal. It has always been my desire to lighten the burden of life for those less fortunate...." It was Gow, our zoo-man—a big, ugly son-of-a-gun from a Terran colony on Mercury. His hands, holding the curtains apart, had thick black hair on them and were not much larger than the hams of a Venusian swamp-rhino. Beamish cleared his throat and said, rather stiffly, "Gertrude?" "She's the star attraction of our show, Mr. Beamish. The only other one on the Triangle belongs to Savitt Brothers, and she's much smaller than Gertrude." I said tactfully, "We'd have to have at least a hundred U.C.'s." He dragged out a roll as big as my two fists, peeled off half a dozen credit slips, and laid them on the table.
output:  Shannon is prone to suspicion after being hunted down by people they owe money to, and thinks Beamish is one of them.
options:  The sound of the chair being pulled back sets him on high alert.  He sees that Beamish has something in his hands.  Shannon is prone to suspicion after being hunted down by people they owe money to, and thinks Beamish is one of them.  Beamish tells them he's there to collect money from them.