In the season seven premiere the Hound stared into some flames and had a vision of things to come (with no spoiler alert, which was pretty rude of the Lord of Light, imho).
“Where the wall meets the sea,” he said, “The dead are marching past.” Many people assumed this meant the dead would make their attack at Eastwatch by the sea, a castle on the wall’s easternmost side Jon Snow sends Tormund and his troops to man and, if necessary, defend from the white walkers.
A keen-eyed redditor noticed a small change in the elaborate opening credit sequence that might explain what the white walkers are up to. Here’s a still from the opening credits of season six showing the wall
Now here’s the same location from the season seven opening credits, notice anything different?