To this, John's mouth twists with exasperation.

"I know cows," he says, more darkly than cows probably deserve. "Migraines the moment I try to call up a cow fact. For me, they're up there with the secrets of the universe. Don't write them off just yet."

He's clearly fucking around, but the hard lines at the edges of his smile are real. It's been a long string of headaches since arrival.