posters, and Joker cards. The Blu-ray disc version additionally offers interactive elements describing the production of some scenes. A separate, limited-edition Blu-ray disc set came with a Batpod figurine. The Dark Knight sold 3million copies across both formats on its launch day in the U.S., Canada, and the UK; Blu-ray discs comprised about 25%–30% of the sales—around 600,000 units. The film was released at the beginning of the Blu-ray disc format; it was considered a success, breaking Iron Mans record of 250,000 units sold and indicating the format was growing in popularity. In 2011, it also became the first major-studio film to be released for rent via digital distribution on Facebook. A 4K resolution remaster, which was overseen by Christopher, was released in December 2017 as a set containing a 4K Ultra HD Blu-ray, Blu-ray disc, and digital download, as well as special features from earlier releases. Merchandise and spin-offs Merchandise for The Dark Knight includes statuettes, action figures, radio-controlled Tumbler and Batpod models, costumes, sets of Batarangs, a limited-edition Grappling Launcher replica, board games, puzzles, clothing, and a special-edition UNO card game. A novelization written by Dennis O'Neil was released in 2008. A direct-to-DVD animated film, Batman: Gotham Knight, was released in July 2008. It was directed by Bruce Timm and includes veteran Batman actor Kevin Conroy reprising his role. Gotham Knight presents six vignettes, each of which are animated in a different artistic style, set between the events of Batman Begins and The Dark Knight. A video game adaptation, Batman: The Dark Knight, was canceled due to development problems. The Dark Knight Coaster, an indoor roller coaster, opened in May 2008 at Six Flags Great Adventure in Jackson Township, New Jersey. Costing $7.5million, the long attraction places riders in an imitation of Wayne Central Station in Gotham City as they move through areas that are vandalized or controlled by the Joker. Themes and analysis Terrorism and escalation A central theme of The Dark Knight is escalation, particularly the rise of the Joker in response to Batman's vigilantism. Batman's vigilante operation arms him with high-tech military equipment against common criminals, and the Joker is the inevitable response and escalation of lawlessness to counter Batman. Critic Siddhant Adlakha considered the Joker an analog for countries such as Iraq, Somalia, and Lebanon, which were targeted by U.S. military campaigns and responded with escalation using terrorism. Batman also inspires copycat vigilantes, further