"Baghead" is the most amiable sort of Frankenstein monster, a film that wonders what would happen if you stretched the skin of a slasher flick over the bones of the ultra-low-budget "mumblecore" esthetic. The movie's cheap, it's clever - it's even a little scary in places. And it's over in 84 minutes. "Saw" fans expecting a gory fright night will hate the thing. I loved it.
The film comes to us from the Duplass brothers, Mark and Jay, who made 2005's "The Puffy Chair," and it costars Greta Gerwig, the slacker ingenue of Joe Swanberg's "Hannah Takes the Stairs" (2007). "Baghead" shares with those movies a lot of wobbly digital-video camerawork, improvised performances, ambience in place of plot, and characters who are hip post-college dolts - charming but clueless.
The film opens with a wickedly funny insider take on film festival Q&A sessions, after which the principals - four out-of-work Los Angeles actors - repair to an isolated cabin to write their own screenplay. Inspiration quickly gives way to alcohol consumption and badly timed flirtation; like their filmmaking colleagues Swanberg and Andrew Bujalski ("Funny Ha Ha"), the Duplasses are beat poets of entropy.
Matt (Ross Partridge) is the lanky type-A stud of the group, while his recent ex-girlfriend Catherine (Elise Muller) is one of those willowy California blondes just beginning to age out of babe consideration (to compensate, she's taking a pole-dancing class). Matt's best friend Chad (Steve Zissis) is the chubby clown, hopelessly in love with the younger and much dumber Michelle (Gerwig), who in turn has her eye on Matt.
The screenplay idea they settle on, based on a drunken dream of Michelle's, is simplicity itself: A guy with a paper bag on his head is running around the woods killing people. It worked for "Halloween" and "Friday the 13th," didn't it? Fame and DVD profits all around, right? The creation of Baghead, however, seems to have willed him into actual physical being. That, or one of the four may be jealously pranking the others.
The Duplasses want to have their cake and eat it, too, and darned if they don't pull it off for much of the film's running time. "Baghead" is a sly parody of gutbucket slice-and-dice horror movies, but not in a jokey "Scream" way - instead, it goofs on the kinds of LA bottom-feeders who think up these movies. (It's also gore-free, if that's what's worrying you.) The movie features almost every slasher cliche you can think of - the doomed slut, the gratuitous topless scene, the shaky madman-in-the-woods POV shot - but delivers them with an offhanded, fly-on-the-wall indie style that deflates the genre's tires.
This is different from a movie like "The Blair Witch Project," to which "Baghead" has been wrongly compared. That left-field 1999 hit used the new videocam mentality to re-create the same old campfire scares; it very much wanted to be taken seriously and thus fooled millions of credulous young moviegoers. The Duplasses are mischief-makers by comparison, delighted to be reverse-engineering an actual plot for a change.
At times, "Baghead" seems designed to make certain kinds of moviegoers extremely angry. Gorehounds will have no patience for it, and you have to have a taste for slow, stammering character improv in which nothing seems to happen. The humor, and it's there, bubbles up in the spaces between what these chuckleheads want and what they're capable of. The actors play along beautifully; a passing shot of Catherine wearing her night-braces to the breakfast table says everything about the vanities of a Hollywood extra. Gerwig is especially funny; her Michelle is an infantile cluck who seems barely to have evolved past the amphibious stage.
The film's final moments, in which everything is tidied up and explained, are a disappointment, but only if you're expecting something long-lasting like art. The Duplasses make ephemera, and their lack of ambition is cheering in a cutthroat business like the film industry. The brothers discover something odd, too: A long shot of a guy standing in the woods with a grocery bag on his head really is frightening, in and of itself. "Bag-head" takes the horror genre apart until it finds the unsettling, irreducible engine at its core. Then it shrugs and walks away.
Ty Burr can be reached at tburr@globe.com.