Toby's "wish" was an anticipation of Dr. Slop's hobby-horse notion that forceps were the answer to everything; Dr. Slop was about to say that he didn't understand how people managed to get born, and Toby said that the armies in Flanders had many men in them. His commonsense attitude stands out in sharp contrast to both Dr. Slop's and Walter's fixation about the delicacy of the brain; he whistles "Lillabullero" when Walter suggests that people born naturally, without help of forceps, are mentally defective. Uncle Toby obviously thinks faster than we give him credit for.
The scenes in which Walter reaches for his handkerchief with the wrong hand may seem to be merely humorous trivia; they are that, but they serve another important purpose as well. All he had to do was put his wig back on his head, take it off with his left hand, and take his handkerchief from his right pocket with his right band. But not Walter Shandy. This is the physical counterpart of his intellectual gymnastics: everything is twisted around as needed to fit in with his hypotheses, and once he sets out with his left hand, he intends to succeed. Somehow he manages to, but the process is unnatural, Tristram suggests.
Walter's movements are described so that we can imagine every second of the contortions and feel the ridiculousness of the situation.
