A dream about a particular animal often means that certain qualities of that animal are significant to you right now.
Think of what that animal symbolizes to you, and what the standard ideas about the animal are. For example, a mule is usually thought of as stubborn).
Notice what the animal is doing in the dream, and how they are doing it. For example, a dog who is digging a hole may mean that treasure lies in hidden places and you'll need to go looking for it.