"Jennifer's Body," the second screenplay from Diablo Cody following her Oscar-winning debut smash "Juno," is so chock full of her quirky trademarks, it almost plays like a parody of something she'd write.

The self-consciously clever dialogue, the gratuitous pop-culture references, the made-up phrases intended to convey a specific high school ethos — they're all there. Even though fembot Megan Fox is an excellent fit to spit out these witty quips, it's all so familiar, it makes you wonder whether Cody has any other weapons in her arsenal.

Part of the allure of the Showtime series Cody created, "The United States of Tara" — beyond the versatility of its fabulous star, Toni Collette — is the humor she finds in everyday suburbia, the reality and the absurdity. And that's actually the best part of "Jennifer's Body," too.

Never mind that it's a mash-up of horror flick and teen comedy: When her characters are talking about regular stuff like toxic female friendships, awkward adolescent sex and high-school dances, it's funny in a relatable way. It's when Cody tries too hard to dazzle us that she loses her footing; meanwhile, director Karyn Kusama ("Girlfight," "Aeon Flux") struggles in her own way to find the right tone amid these two divergent genres.

The result: "Jennifer's Body" is never scary and it's only sporadically amusing.

Fox is a great choice, though, to play Jennifer, the queen bee who longs to flee the small town of Devil's Kettle. Here, the "Transformers" star gets to show what she can do when given the chance to speak, and not just run from angry, shape-shifting trucks in a tight denim miniskirt. Granted, playing a sexy, popular cheerleader probably wasn't a huge stretch for her, but hey — it works.

One night, after attending a concert by her favorite band that goes disastrously awry, Jennifer seems ... different. This is immediately obvious to her childhood best friend, the nerdy Needy (Amanda Seyfried, rendered vaguely mousy beneath glasses and stringy hair). But eventually the whole town realizes something is wrong when boys' bodies start turning up bloodied and eviscerated.

Jennifer, meanwhile, is more radiant and confident than ever — and strangely indifferent to the campus-wide catharsis in which everyone else is wallowing, a group-think phenomenon that was parodied so well in "Heathers" and the recent "World's Greatest Dad."

Trouble is, we all know what the deal is. There's no mystery to engage us, no real frights to jolt us, just a waiting game until the rest of the town catches on.