Montomorency, the fourth member, is treated as an equal with a personalityof his own. How does the writer describe him and his antics?

Montmorency is an intelligent Fox Terrier who acts as a fourth character in the book. He is assertive and frequently acts as a character foil to the men's inept outdoor skills,

"Montmorency’s ambition in life is to get in the way and be sworn at. If he can squirm in anywhere where he is particularly not wanted, and be a perfect nuisance, and make people mad, and have things thrown at his head, then he feels his day has not been wasted."(chapter 4)