The expression "bark shrilly" could be substituted by many other synonyms, depending on the context. For instance, one could say "yelp loudly," "howl piercingly," or "screech sharply." Other options might be "shriek stridently," "squeal shrill," or "squawk loudly." These words all convey a sense of piercing, high-pitched sound, which could be used to describe a dog barking or a person shouting. Using synonyms can help to add variety and interest to one's writing or speech, and help to paint a more vivid picture of the scene being described.