Here the making of the last episode of Game of Thrones released last week, Season 5 episode # 8.
This is one of the most important scenes of episode 8: The Massacre at Hardhome (HBO).
In the Making of we can see the techniques used to create the interaction scenes with the undead and the fearsome Strangers, used the green screen technique to work on the body parts of the actors.
** Warning: it contains spoilers for those who have not yet seen the episode!