"He follows him around like a little puppy dog."
People, it's a puppy or a dog, not a puppy dog. Do you also say, "Look at the cute kitten cat?" You probably do, don't you? After all, this is the internet and it goes where none have gone before -- even to your house.
Doe deer, colt horse, chick chicken. We say none of these things yet we stick with "puppy dog".
This kind of phrasing is from the same mental neighborhood as a term used by the police. When looking for a body, they always like to bring along a sniffer dog.