Men are Pygs.

That’s at least one potential take-away from “Ruby Sparks,” an adroit, modestly inventive take on the Pygmalion myth from the actress Zoe Kazan. Kazan wrote the screenplay for this alternately fizzy and cerebral romantic comedy in which she also stars. That “Ruby Sparks” just happens to offer a showcase for some bravura acting on her part – particularly in one show-stopping sequence late in the proceedings – only proves that Kazan is as cognizant of the limited roles for women in Hollywood as she is willing to take matters into her own considerably watchable hands.

If “Ruby Sparks” ultimately loses its nerve, perhaps that’s Kazan’s sop to audiences she thinks won’t be interested in dealing with the tougher implications of what they’ve just seen. Because for a while there, “Ruby Sparks” is a tough little movie.

Paul Dano plays Calvin Weir-Fields, a novelist who had a hit book when he was 19 and now toils alone in a posh home office, suffering a massive case of writer’s block as he tries to match his early promise. Inspired by a dream, he begins noodling with a character who, as he pecks away at his vintage typewriter, swiftly becomes a fictional romantic ideal: Ruby Sparks, a wide-eyed, hip, uncomplicated artist who, like all awesome girlfriends, reflects Calvin at twice his size, charm and intelligence.

When Ruby unexpectedly comes to life – in the red-headed, azure-eyed form of Kazan – Calvin initially think she’s a figment of his needy imagination. But when it turns out other people can see her, too – including Calvin’s no-nonsense brother Harry (Chris Messina) – he’s forced into an increasingly provocative series of challenges having to do with projection, control and unconditional love.

The film’s directors, Valerie Faris and Jonathan Dayton, keep its narrative lines as clear and uncluttered as Calvin’s pristine, white L.A. house. Like their last outing, “Little Miss Sunshine,” Kazan’s “Ruby Sparks” traffics in its share of well-worn indie tropes. But Faris and Dayton mostly resist easy cliches, although Annette Bening’s characterization of Calvin’s groovy hippie mom in Big Sur borders on hackneyed caricature.

“Ruby Sparks” is at its best when it puts viewers in the highly charged emotional petri dish of the relationship between Calvin and Ruby, who understandably begins to chafe at the author’s attempts to write her into his own, self-valorizing script. And Kazan manages to mount a clever critique of the very dream girl image she embodies, taking it to its most absurd extreme in a biting, be-careful-what-you-wish-for climax. Dano and Kazan, a real-life couple, bring unforced verisimilitude to their portrayal of the alternately idyllic and embattled young couple, although Dano’s lanky, long-limbed feints and fumbles aren’t nearly as interesting as what is going on behind Kazan’s all-seeing kewpie-doll eyes.

Perhaps it’s because “Ruby Sparks” fizzes along with such promise that its finale lands with such a quizzical thud. Kazan winds up indulging in the very wish-fulfillment she initially sets out to deconstruct. For a movie so bent on skewering illusions, “Ruby Sparks” ultimately can’t entirely let go of its own.