Huck is hunting with Buck Grangerford, who tells Huck to jump into the woods when they hear someone coming on a horse. The man, who is dressed like a solider and has a gun, turns out to be Harney Shepherdson. Huck hears Buck's gun go off, and he sees Harney's hat fall from his head. Huck and Buck take off at a run, and when they return home, Buck's father seems pleased that Buck shot at Harney, though he wishes that Buck had shot at Harney in the open.
Later, after he finds out about the senseless feud between the Grangerfords and Shepherdsons and when Sophia Grangerford is running off with Harney Sheperdson, Huck also climbs a tree during a gun fight. In this fight, Buck's father and Buck's two brothers are shot dead. While he's speaking to Buck, people come after Buck and his cousin, Joe. They are also killed. Huck says, "it made me so sick I almost fell out of the tree" (128). Huck says he can't even tell what happened because it makes him so sick. Huck's reaction is to flee life on shore. He is relieved to be back on the raft, where, he says, "You feel mighty free and easy and comfortable" (page 129).
While Huck is hiding in the cottonwood tree in Chapter 18, he sees the feud between the Sheperdsons and the Grangerfords come to life (or perhaps I should say to death). He sees Buck Grangerford and a cousin of his fighting against a group of Shepherdsons. He sees the two of them end up getting ambushed and having to jump in the river while the Shepherdsons are yelling about killing them and shooting at them while they tried to escape.
Huck is revolted by what he has seen. He says that he will never be able to rid himself of the images.