1) The situation of an absence of horse-bodied men from the old English city of Oxford.
2) An exclamation caused by a ridiculous long-term belief being realised to be impossible.
1) "I haven't seen any of those horse-bodied men about this city of gleaming spires lately..."
"Well of course, there are no centaurs in Oxford!"
2) "What?! The Moon isn't made of cheese
"Isn't that obvious
? There are no centaurs in Oxford!"