Pixomondo has released a video via Wired giving a detailed look into how the CGI dragons were created for season 3 of Game of Thrones.
The Wired article also has a few additional details and quotes from Pixomondo animator Sven Martin:
While filming, Emilia Clarke, who plays Daenerys, initially used puppet stand-ins called “stuffies” and even a tennis ball on stick to help create a sense of physical interaction. Martin says that they wanted her relationship with Drogon to seem almost maternal; “when she’s stroking him, he should be a little bit like a cat.” When strangers, approach, however, Drogon can turn quickly from housecat to monster, baring his teeth in a way that reminded Martin “a bit of the Alien Queen, which even for me was very threatening.
Winter Is Coming: Don’t mess with Dany, y’all. She’s got tennis balls on a stick and she’s not afraid to use them! Seriously though, this is a cool vid. It’s impressive to see just how much time and effort was put into getting the dragons just right. All that hard work paid off, as the dragons were nothing short of feature-film quality.