Are you reading Game of Thrones? Bran and Summer are my favorite characters. I'm also super excited for the new season. Sorry for fangirling here's the answer to your question: - Would have means something you wanted to do but didn't - Should have means something that would have been a good idea, but that you didn't do it. It's like giving advice about the past when you say it to someone else, or regretting what you did or didn't do when you're talking about yourself. So in this case the pup already opened it's eyes, an event that happened in the past, should have is incorrect here because the sentence doesn't refer to an idea or action that you regret. For example, "I should have studied harder! (= I didn't study very hard and so I failed the exam. I'm sorry about this now.)"