What does Twain satirize in his description of church service and the hogs that sleep under the floor in The Adventures of Huckleberry Finn?
I assume that you are talking about the very brief description in Chapter 18 of the service that Huck attended with the Grangerford family.
In that description, Twain is mainly satirizing the idea of using a feud as a way of defending one's family honor. He is making fun of the idea that Christians could do this. He points out how the sermon was all about brotherly love and how the family praised the sermon very much on the way home. But all the time, they had their guns between their knees. In addition, the very next day, some of them would be dead because of the feud.