Symmetric Presupposition Satisfaction Is Mid-sentence Presupposition Correction

Why was it acceptable for me to utter this sentence, which contains the presuppositional expression my hamster? Presumably it’s because the sentence presupposes that I have a hamster; and a sentence with this presupposition is acceptable in any context like the one we’re in, where you and I come into the conversation sharing the belief that I have a hamster. It could also be that you didn’t know that I had a hamster, but I told you: “I have a hamster. Tomorrow I’m taking my hamster to the vet.” So then it’s not necessary that we begin the conversation both believing that I have a hamster: it’s enough that, before the sentence containing the phrase my hamster is uttered, we both believe that I have a hamster. But beliefs are fickle creatures. What happens if I start a sentence, and then something happens in the room while I’m talking? If you and I witness the event, our beliefs will change, and the context changes accordingly. For instance, imagine I say: