“No urns,” he said at last.
“What urns?” said Nobby.
“Nude women are only Art if there’s an urn in it,” said Fred Colon. This sounded a bit weak even to him, so he added: “Or a plinth. Best is both, o’course. It’s a secret sign, see, that they put in to say that it’s Art and okay to look at.”
“What about a potted plant?”
“That’s okay if it’s in an urn.”
— Thud (2005), Terry Pratchett