To determine the appropriate toy size for a specific dog breed or cat, consider the pet's size and chewing habits. For dogs, choose toys that are large enough to prevent choking but not so large that they are difficult to play with. Avoid small parts that can be swallowed. For cats, select toys that are lightweight and easy to bat around. Ensure strings and small components are secure to prevent ingestion. Always supervise playtime initially to ensure the toy is safe and appropriate for the pet's size and behavior.