It's no kind of excuse. It would have just been a funny pun. You are still talking out of your ass. Regardless of the pun a bird is a bird, not a rat. They are no more a real rat than we are and a pun doesn't change that at all. All the other rat merchants were rats. We did not expect this because here was no reason to expect a bird. There would have been no "you should have expected this" because it was never implied. It would have been "haha I get it". It's a minor thing at most and all that would have been different was that the joke would have had two layers for those who spotted it.