The ruby at Melisandre's throat gleamed red. "It is not those foes who curse you to your face that you must fear, but those who smile when you are looking and sharpen their knives when you turn your back. You would do well to keep your wolf close beside you. Ice, I see, and daggers in the dark. Blood frozen red and hard, and naked steel. It was very cold."
"It is always cold on the Wall."
"You think so?"
"I know so, my lady."
"Then you know nothing, Jon Snow," she whispered.

Author: George R.R. Martin