Montmorency the member of the boat has a personality of his own. How does the writer describe his antics

Montmorency is a Fox-terrier. Being a minor character and a dog in a comedy, we are not going to have a complex set of traits. He gets into all kinds of shenanigans, which irritate and entertain the three friends. Jerome says of Fox terriers:

Fox-terriers are born with about four times as much original sin in them as other dogs are, and it will take years and years of patient effort on the part of us Christians to bring about any appreciable reformation in the rowdiness of the fox-terrier nature.