Batman: The Killing Joke
Batman: The Killing Joke director Sam Liu explained that the movie's 'sex and psychological torture' is the reason it earned an R-ratingDC Entertainment/YouTube

Batman: The Killing Joke made its debut at San Diego Comic-Con (SDCC) at the weekend and screened for two consecutive nights in selected cinemas in both the UK and the US from 25 July. So far, the feature-length animation has received mixed reviews, with some fans questioning why the film warranted an R-rating, despite its expected darkness while staying true to the controversial source material.

During the convention (21 - 24 July), director Sam Liu explained to ComicBook.com why he believed that Batman: The Killing Joke having such an adult-aimed rating was necessary. And as it turns out, it wasn't just because of the violence...

"I think we weren't even thinking about [the rating] at the beginning. [Executive producer] Bruce [Timm] and I, when we had built it up in animatic form, we thought it might get a PG-13, because it's not extra-gratuitous. The psychological stuff is, I think – the R comes from a certain amount of responsibility. It is really dark.

"Any time you have psychological torture, that starts going into this questionable area," he explained to the publication. "We've had many films where people get shot and there's blood, things that make me think we're going to get an R-rating! For whatever reason violence is – there's a certain desensitization that's happened. That's not as shocking anymore. But for some reason, sex and psychological torture is more touchy ground."

Batgirl in Batman: The Killing Joke
Writer Brian Azzarello's treatment of Batgirl has become a controversial talking point since the animated film debuted at San Diego Comic-Con last weekendWarner Bros. Pictures

Released in 1988, Alan Moore's original graphic novel focuses around The Joker's attempt on capturing Commissioner Gordon and making him insane to prove to Batman that even the most well-respected citizen in Gotham can be turned crazy after just "one bad day". Of course, Batman attempts to thwart his arch-nemesis's plans and return him to his prison, but before he can do so, The Joker manages to kidnap Gordon and shoots and paralyses his daughter, Barbara Gordon aka Batgirl (who later becomes Oracle following her injury, as DC Comics fans will already know).

But writer Brian Azzarello was keen to give Batgirl more to do in the film, so set about fleshing out her story within The Killing Joke. The end result being the creation of a questionable romantic relationship between The Dark Knight and librarian Barbara, where the latter assumes the role of Batgirl in order to impress Batman – a thread which didn't go down all that well with DC lovers.

In the animated picture, Star Wars actor Mark Hamill lends his voice once again to The Joker while Kevin Conroy (Justice League: The Flashpoint Paradox) portrays Batman. It will be available to purchase on Blu-ray in the US from 2 August. It will be released in the UK on the 8th.

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