A big dog and a smaller dog fight over a piece of fabric.
Two dogs fighting over a piece of fabric
If there is a big dog and a smaller dog, there are two dogs.
When you add together the number of dogs mentioned in Sentence 1, "a big dog" and a "smaller dog", you get a total of two dogs. In both sentences the dogs are fighting over a piece of fabric.
Same big dog and smaller dog refers to same two dogs.