Moose Maddon bullies Cecil throughout the story. At one point, Moose throws Cecil, while Cecil is sleeping, into a river, and Cecil nearly drowns. The other men working with Cecil and Moose notice that "jokes" like this seem to have a conspicuously "grim purpose." The implication of the word "grim" is that these "jokes" are not simply harmless fun but are intended to seriously hurt, or maybe even kill, Cecil. Maddon seems to have a "personal vendetta" against Cecil.
Cecil confides to one of the other men, Mr. Anderson, that he is afraid that Moose will one day "really hurt" him, and Mr. Anderson acknowledges that he is "afraid of the same thing" himself. Indeed, Mr. Anderson says that Moose's urge to hurt Cecil seems to be "almost insane." Cecil tells Mr. Anderson that he is convinced that Moose "wants to kill" him.
At the end of the story, we are told that Maddon's body is discovered, dead, at the bottom of a ravine. His death is recorded as accidental, but Mr. Anderson notices "burn marks" on the trunks of two trees, which he thinks, "could have been made by wire loops." The implication is that Cecil, who likes to make things out of wire, deliberately set up a trip wire, near the ravine, to trip Moose. The fact that Cecil probably killed Moose is probably the best evidence that Cecil really did believe that Moose was going to kill him. Cecil killed Moose before Moose could kill him.