Ralph and Jack respond differently to the "beast". Ralph, when he first hears of a beast from the air, the dead parachutist, in chapter 6, is fearful. Sam and Eric have described what they thought they saw and their fear is contagious. Ralph fear is logical - a beast could hurt them. Ralph realized that the beasts that the young boys mentioned earlier were not real beasts; they were just manifestations of the boys' imaginations. Then, later, in the last chapter, when he encounters the pig's head on the stick, he comes to realize what Simon and Piggy knew much earlier, that the beast was in each of them, not in any outside force or entity. Jack also knew the littluns' talk of beasts was just imagination talking in the early chapters. He is excited though when he hears Sam and Eric describe what they've seen. He wants to hunt it down. Jack also realizes that the beast, and the fear it invokes, could prove useful to him. He sees it as a tool he can use to his advantage. Later, when he performs the sacrificial ritual of putting the dead pig's head on the stick as an offering to the beast, he shows that he has come to believe in the beast himself. But, unlike Ralph, Jack feels he can control the beast by making sacrifices to it.
Ralph and Jack both respond to the beast differently throughout the novel. Ralph is skeptical of the beast when he first hears about it from the littluns. He holds an assembly to pragmatically respond to the issue of identifying the beast and tries his best to understand it. However, when Samneric claim that they witnessed the beast firsthand, Ralph becomes worried and reluctantly follows Jack on a hunting expedition in search of the beast.
Similar to Ralph, Jack does not initially believe that a beast exists. However, when Jack mistakes the dead paratrooper for the beast, he becomes frightened. Jack sees that the boys are terrified of the beast and uses their fear to his advantage. Jack begins to manipulate his hunters into carrying out rituals and sacrificing a pig's head to appease the beast. He elevates his position of power and importance by claiming that he will protect his hunters from the beast.