Pets in a story are another way to add humor. Be sure to give the animal a personality, though. Its presence alone isn’t sufficient. Otherwise it won’t have any more impact than a picture on the wall or a random joke.
Being an integral part of the story is even better. Animals, at least to those who love them, are endearing and teach us about life in subtle, nonverbal (obviously) ways. A story written from a pet’s point of view can be particularly humorous.
Another benefit of including an animal or pet is that it can help sell it to those who are also fans of that particular critter. Some authors have done very well capitalizing on this trick. Give it some thought how it might add another dimension to your story.