Once there was a dog.
In the second sentence, it was a canine.
By the third sentence, it was a mutt.
After that, the poor writer couldn’t choose between hound or pooch.
Why couldn’t he just call it a dog again?
Well, at some point — maybe in Grade 6 Language Arts or Grade 9 English — his teacher told him not to keep repeating the same word. And then another teacher came along and said the same thing.
And you know what? It is good for kids to get familiar with the thesaurus and learn different ways to say things. Part of being a kid is learning new words.
But adults aren’t kids any more. If you’ve made it to adulthood as a native English speaker, you probably know quite a few words by now. (In fact, your brain probably holds about 10,000 to 20,000 words.)
Now that you know that many words, you can make decisions about which ones you choose. In general, it’s probably clearest to call a dog a … dog.
After all, no two words mean exactly the same thing. A mutt implies that the dog might have questionable parents, a hound makes me think of a very big dog (no small hounds allowed), and a pooch appears in my head as some kind of slobbering dog. Canine is actually an adjective and not a noun.
All that to say: put your thesaurus down. Choose your word and stick with it. Don’t make your reader wonder why you just chose a new word.
Once there was a dog and it continued to be a dog. The End.