Warning: spoilers for season seven of "Game of Thrones," up to episode five ... number of ways to kill the dead. Thankfully, Valyrian steel is one way to kill the White Walkers.

For instance, Cregan Stark bore the Valyrian steel blade Ice, the same one that Ned Stark would wield over 100 years later on Game of Thrones...before it's used to behead him at the first season.