The parody of Teeth isn't subtle, though it is, for a few moments, cute.
Nestled near nuclear plant smokestacks, a small suburban home holds secrets. Though not exactly revealed in the opening shots of Teeth -- which show an innocuous fence, lawn, and wading pool -- the trouble is hinted at by a bleak and pounding soundtrack. As the camera descends and closes in on a small family unit, the arrangement becomes clear: single mom Kim (Vivienne Benesch) has married single dad Bill (Lenny Von Dohlen), and seated in loungers while sipping cool drinks, they gaze on their adorable children, plopped down in the pool before them. It's all so ideal and strained, it can't possibly last.
Just so, within minutes, the serenity is shattered when little Brad pokes his finger where it shouldn't go and feels the pain of his stepsister's mystery, and the film's titular premise. With his bloody, now topless finger held up in front of Dawn's adorable, vacant smile, the scene cuts first to credits over some microscopic comedy (deviant eggs devour pushy sperm), then to several years later, when preschool Dawn is grown up to be high school Dawn (Jess Weixler), lecturing to children on the virtues of abstinence. "We have a gift," she says earnestly, the camera framing her wide, pretty, pale face, "A very precious gift." She urges the girls (and the boys too), to "keep your gift wrapped," to preserve it until after marriage. Ah, the perfection of such sentiment.
The parody of Teeth isn't subtle, though it is, for a few moments, cute. The central "gag" is clear early on -- Dawn's own "precious gift" is mutated into a literal vagina dentata, of which she has incomplete knowledge. That this knowledge will soon become more complete is indicated when, among the upturned faces of her eager young audience, the camera also picks out her most enchanted listener, her new classmate Tobey (John Hensley). It's not long before they run into the problem you anticipate. Tobey cautions her that he's actually had some experience before he moved to town, and try as she might, poor repressed and conditioned Dawn is unable to resist her own adolescent urges. During an afternoon date, she and Tobey swim in a (remarkably clean) river near a cave with overhanging formations that directly denote the horror he will soon be disciplined: sure enough, his efforts to share his earnest, urgent affection with her result in bloody mayhem.
Dawn's response to Tobey's castration appears both exaggerated and antic: as he roars in pain and scrambles away in search of help, she cowers against eth cave wall, the penis limp and red on the ground before her. Her gaping mouth and crumpling form suggest not only Dawn's own indoctrinated ignorance regarding her body (this point underlined by the high school biology books with penises visible and vaginas covered over by stickers, an event that filmmaker Mitchell Lichtenstein says is inspired by a "true situation" at a Virginia school in 2000), but also her effort to stay unaware. It's hard to know and feel responsible, and so she tries not to.
The film goes on to insist on her lack of responsibility, at least at first. While this tack makes the case that women are often "subjugated," it also indicts the men who write the textbooks, make the rules, and arrange the marriages so that property and legacy rights may be maintained. Dawn's version of containment is premised on her fear of knowing (as when she refrains from investigating her vagina, troubled by visions of punishment: that her body is the punishment is a rudimentary joke). As distressed as Dawn is over Tobey, her turning to other men for help and sympathy only indicts them, as they take advantage of her seeming vulnerable state. These include a lascivious classmate and a gynecologist, Dr. Godfrey (Josh Pais), whose decision to probe her without a glove ordains him as a deserving victim of the worst Dawn's teeth can deliver; his mangled hand and screaming are treated as broad comedy.
Similarly, Dawn's interaction with her stepbrother Brad (grown up to be John Hensley) becomes a crude cautionary tale. Tattooed, drug-addled, foul-mouthed, and fond of very loud music, Brad keeps his big mean dog (named "Mother") in a cage in his bedroom, where he also entertains his plainly stupid, trashily sexy girlfriend. He also maintains an unhealthy interest in his stepsister, for which he will pay dearly. Dawn's daily anguish over Brad's bad behavior is exacerbated by their parents' preoccupation with Kim's illness. Bedridden and ashen, she provides little in the way of a life model for Dawn, except perhaps that being a girl means being sick. While Bill worries over her, the kids are left to fend for themselves, their opposite "personalities" contrived and tedious, leading exactly to the end you imagine (and involving Mother the dog).
Lichtenstein has told various interviewers that he was inspired by a class he took some years ago with Camille Paglia, whose self-presentation is famously outrageous, a means to publicize her general argument with the world's gender and sex arrangements. While such argument is surely still relevant, given the many ongoing repressions and horrors inflicted on women every day, the analysis here is dated and, however intentionally, primitive. Dawn's coming to consciousness may be cause for celebration, as you imagine all the bad men who will suffer terrible consequences. As a fantasy, it has obvious limits.