I don’t really like it when movies feel the need to explain everything.
Spoilers.
Dawn is a young woman, who is a purity ring activist. This has lead her to be somewhat unfamiliar with her own body. She also happens to have what is known as vagina dentata, meaning a she has an extra set of teeth as a protection in her vagina. When she feels threatened down there, the teeth come out.
How do I know this condition is known as vagina dentata? Because the movie uses that name numerous times. Worse yet, it needs to explain what it means and the supposed reasons for the birth of this myth. Sure, this is all interesting, but its also unnecessary exposition. We understand quite well what’s going on here. At least on a subconscious level.
The myth of vagina dentata is basically the result fear of the unknown regarding vaginas. In much the same way you would think twice about putting your hand into a dark hole, the vagina is mysterious to the men. While unnecessarily explicit porn has made them somewhat less mysterious in recent times, for teenagers there’s still enough uncertainty about the whole deal that it is a source of fear.
The thing is, religious norms have pushed the females into a similar situation. The anatomy textbooks they have were censored specifically regarding the anatomy of vaginas. And even after Dawn removes the sticker used for the purpose of censoring, the image is not very helpful (it is for Dawn, who specifically wants to compare the image to her own). At least the visualizations we got back in the day were much more descriptive. So, Dawn herself finds her own body mysterious. The teeth are an autonomous defense mechanism. They act if they feel threatened.
The ending is kind of difficult for me. Dawn decides to leave town, because she has killed several people at this point. She catches a ride from a random older man, who turns out to be a pervert and Dawn apparently decides to unleash her dentata on him. You could take this in many ways. My initial thought was that this is nicely empowering. Dawn has come to terms with her own body and can now employ it’s mutation meaningfully. That’s a nice ending.
On the other hand, I know certain members of the audience (the incels) would just make their own misogynistic take on this. These people don’t believe that women merit autonomy, so this is an attack against men in general instead of being an attack on specific males (who Dawn just happens to run into several times). I guess it doesn’t help that most of the men in Dawn’s life are pretty horrible.