'Cowboys & Aliens' and more mash-ups

"Cowboys & Aliens," which arrived in theaters Friday, is taking a gamble by blending two disparate genres. Generally speaking, moviegoers like their concoctions straight, not mixed. It's one thing to make a romantic comedy, but a sci-fi-Western? Isn't that like mixing Dr Pepper with Mountain Dew?

Then again, it could result in a taste sensation. Here are five of the riskiest genre-blending movies of all time, some of which exploded and some of which fizzled.

PREDATOR (1987) -- It starts with Arnold Schwarzenegger leading commandos through a jungle, then introduces a heat-sensing creature from outer space. The unlikely combo worked so well it spawned four more films.

AN AMERICAN WEREWOLF IN LONDON (1981) -- John Landis' horror-comedy mixed both genres in equal measure. One minute, the lycanthrope David (David Naughton) is tearing apart a victim, the next he's chatting with his undead, rotting friend Jack (Griffin Dunne). Still a classic.

BRICK (2005) -- Joseph Gordon-Levitt, Meagan Good and Lukas Haas star in this brutal film noir set in high school. The characters even speak their own hard-bitten teenage slang: "Where you been eating?" Terrific reviews did not equal box-office success.

SCOTT PILGRIM VS. THE WORLD (2010) -- Michael Cera stars as an indie-rock slacker and superhero in this cross-cultural, multigenre mash-up. Though fast-paced, funny and wildly inventive, it proved too much even for today's multitasking youth.

BEHIND THE GREEN DOOR (1972) -- An unlikely mix of art-film (nonlinear narrative, weird color schemes) and hard-core porn (no explanation needed), it became a mainstream hit and launched Marilyn Chambers to stardom. Then again, mixing any genre with sex is hardly a commercial risk.