Bobbing up-and-down

The use of repetition has been a major part of Kurt Vonnegut's novel. Many phrases are noticeably repeated over and over again throughout this book. One of these phrases is the phrase, "bobbing up-and-down". In the war, 'bobbing up-and-down, up-and-down, Billy beamed lovingly at a bright lavender farmhouse that had been spattered with machine-gun bullets"(65). The uneven soles of Billy's shoes cause him to walk awkwardly, but there must be more significance to these repeated words.
Repetition was also a large part of our previous book, Night By Elie Wiesel. On page 64, Wiesel wrote, "never shall I forget that night, the first night in camp, that turned my life into one long night...".  The phrase "never shall I forget" was repeated four other times. In this case, I think that the reasoning behind this repetition was to create an emotional connection with the reader and to emphasize the power and hardship of what the author went through.
Even though the reasoning behind Wiesel's repetition was quite clear, the thinking behind the repetition in Slaughterhouse Five is not always apparent to the reader.
As I try to compare the repetition in Slaughterhouse Five and Night, I find it a little difficult because it was clear that repetition was used in Night for emphasis and so that these horrific events would resonate with the reader. However, can this same reasoning be applied to Vonnegut's repetition? If it is applied in the same way, why would he be trying to have Billy's "up-and-down" motion resonate with us?
Do these words help to enforce Billy's strange personality? What is the importance of this repetition? Is there a significant between the two extremes of the words "up" and "down"?