Game of Thrones season 6 spoilers below, of course.
Miguel Sapochnik directed the final two episodes of Game of Thrones season six, and he's been full of little details about how the show gets made. Most recently, he revealed the most challenging part of filming the season finale. In a series that deals with lots of sex, murder, and CGI to create special effects, it was a actually simple-seeming scene that proved difficult to film, thanks to certain time constraints.
According to Sapochnik, the toughest scene involved Grand Maester Pycelle and his demise at the tiny hands of eight tiny children working for ex-Maester Qyburn, also known as his "little birds." The reason it was so hard? The kids (thankfully) didn't know how to make a realistic stabbing motion with their stage knives:
When you give eight kids rubber knives and ask them to stab a blood bag, it’s not only somewhat disturbing to watch but you butt up against reality in which children don’t actually know how to stab something. Sounds silly but suddenly we found ourselves running out of time on the set with our eight kids and realizing that none of them really had much experience with stabbing and so it just didn’t look right.