Think about it. When you come home a dog is wagging his tail at the door and welcomes you home by licking your face. A cat doesn’t care your home. He is napping. A dog loves to play. He will chase a ball, Frisbee, a stick, anything; he runs after it and returns it to you. A cat will just look at you with a look that says, “What do you think I am, some kind of dumb dog. I saw you throw that thing, the dogs gets it, and you throw it again. The dog doesn’t get it, I do. I’m out of here. Time for another nap. Hey you got any catnip man. I need a hit.”
If you give a cat a ball of yarn he will play with it, not for long, and won’t do much with it, because he doesn’t know what to do. A dog won’t play with a ball of yarn. He will have a look on his face that says, “What do you think I am, some kind of dumb cat. Throw me a ball man, not a ball of yarn. I want a real ball.” And if the cat gets tired with the yarn and you have no catnip, he wanders into the bathroom, ignores his litter box, and drops a surprise in front of the toilet, meowing with gleeful laughter.
One time I was pet sitting for my brother who had a dog and cat. The kitty wandered into the living room one evening, his little body looking like he was going to heave, which he shortly did, all over the fluffy red carpet. Did the cat offer to clean up? No. He wandered off to take another nap. But the dog said, “No problem.” He ran over and lapped up the cats digested meal like he was a starving cookie monster with a plate of cookies. Dog is man’s best friend. I loved my brothers dog.
The reason a writer needs to know the difference between them is that if one of your characters has a pet, say like the dog Asta, in Dashiell Hammett‘s “The Thin Man,” make sure the dog or cat has a personality. If you create the pet he must behave in a manner that people can identify with, otherwise why is the dog or cat in the story.
You can even go crazy at times. There was a couple-true story-that kept a buffalo in their house. I have seen pictures and read about them. Now that is another story.