Actually, Ygritte said it more like, “YOU KNOW NUFFIN’ JON SNRRRR.”
But it’s not that Jon Snow anyway.
John Snow, the English Physician is kind of a rock star in epidemiology. He helped find the source of a cholera outbreak in London in 1854. By observation and interviews of affected people and those around them, he was able to trace the outbreak to a public water pump. The city soon shut it down by removing the handle and the epidemic subsided.