Corrected entry: At the wedding, we see an old Ned and Maude Flanders sitting with the guests, even though Maude dies during series 11, years before the wedding.
Corrected entry: Marge is reminding Lisa of the differences between the UK and the USA before she goes to visit Hugh's family in England. Obviously the steak-and-kidney pie remark is a joke, but she says, "Remember, a mile is called a kilometer..." No it isn't. The metric system is used in mainland Europe - miles over here are still miles.
Correction: This is clearly a mistake on Marge's part, as she is unfamiliar with European life and makes things up based on expressions she vaguely remember hearing about. And isn't it possible, since this episode takes place in the future, that the UK has joined the rest of Europe and switched to the metric system?
Correction: Not really a mistake as the "future" event was only a prediction from a dubious fortune teller and not an accurate or precise account of things to come. As the fortune teller told Lisa of her future, what we see is Lisa imagining the story, and seeing as Lisa would not know of Maude's untimely death, she would still assume, as the fortune teller spoke of the wedding party that everyone she knows now would be there.
Mad Ade