There are many ways to entertain your dog when it rains. You can play indoor games such as hide and seek, fetch, or tug-of-war. You can also teach your dog new tricks or commands. If your dog enjoys puzzles, you can buy a puzzle toy to keep them occupied. If your dog is comfortable with it, you can also take them for a walk in the rain. Lastly, you can give your dog a special treat or toy to keep them entertained.