Under Vaughn's dark influence, Grey increasingly changes in disturbing ways, ignoring Charlie's concerns but improving her music skills. Vaughn however is far more of a danger than either realizes, with a personal connection to Grey and her long-standing hallucinations slowly revealed which puts both women in peril.
Examples:
- Abusive Parents: Grey was raised in different foster homes, some of which she indicates had been terrible, with cruel foster parents who'd leave the kids to go hungry at times.
- Alternate Identity Amnesia: Grey had blacked out when she fully transformed and killed Charlie. The very ending's shots of her eating Vaughn's flesh in wolf form imply she was able to control her form now that she realizes what she is.
- Archnemesis Dad: Vaughn turns out to be Grey's birth father. He's a ruthless werewolf who tries to mold her into his image. Grey refuses to go along, and kills him in the end so he can't harm anybody else.
- Bittersweet Ending: More on the bitter side. Vaughn is defeated and gone, the album is finished and an implicit success, and Grey escapes, but she lives with the regret of unconsciously killing her beloved girlfriend and having to kill her birth father, along with the realization she's a werewolf still experiencing the strong desires to consume bloody meat. While the flashes in the ending performance suggest she's more in control of herself, her condition still may well cause her to harm someone else.
- Black Dude Dies First: Charlie is the first main character to die in the film. She's the only person of color in the film, with East Asian ancestry.
- Bloodlust: Grey develops a desire for blood, hence the film title, as part of her meat craving. At one point, she licks up blood from a piece of meat in the refrigerator. Her hallucinations involve this partly as well.
- Car Fu: How Grey kills Vera in the climax, running her over several times to make sure she's dead.
- Domestic Abuse: While influenced by the changes she's undergoing, Grey chokes her girlfriend Charlie before she knocks her senseless by tossing her against the wall. That being said, she quickly regrets it and urges that Charlie leave to save herself. At the time she also clearly isn't in her right mind.
- Evil Old Folks: Vera, Vaughn's elderly housekeeper, appears creepy and cold from the beginning. Then near the end Vera tries to murder Grey, and is a willing accomplice to Vaughn's murders.
- Friend to All Living Things: Grey is a vegan who refuses to eat meat out of concern for animals, and is upset when she accidentally kills a rabbit while backing up her car. This makes her hallucinations of devouring animals while turning into one especially disturbing for her, with an increasing craving to eat meat. She eventually kills a mouse while Vaughn urges her on.
- Gender-Blender Name: Grey and Charlie, who are a lesbian couple, both have gender neutral/boyish names.
- Hallucinations: Grey has had disturbing hallucinations for years of turning into an animal then ravenously eating prey. She takes medication for it, but stops as she dislikes the side effects. They stem from her unknowingly being a werewolf.
- Horror Hunger: Grey, a vegan, experiences the unsettling, intense desire for meat while at Vaughn's house. It echoes her hallucinations of being an animal devouring prey. This turns out to be because she's a werewolf.
- Hunting the Most Dangerous Game: Vaughn hunts down a female hitchhiker his housekeeper Vera procured while in wolf shape, then kills and eats her.
- Irony: Grey, a vegan who stopped eating meat as a child in horror at seeing how it was made, gains an intense desire to eat this later in life.
- Lipstick Lesbian: Grey and Charlie both favor overall feminine styles, although it isn't that intense. They largely just come off as average, putting them in chapstick territory.
- Luke, I Am Your Father: Vaughn reveals to Grey he's her father late in the film, with his wife Greta her mother who gave her up for adoption so she'd be kept from him.
- Lyrical Dissonance: Grey sings a pleasant-sounding, melodious song about her desire to consume meat and blood at the end.
- Minimalist Cast: There are only seven characters in the film, and three only have one or two scenes.
- Monstrous Cannibalism: The shots of the movie's ending reveal Grey in wolf form eating her birth father Vaughn's remains (who's also a werewolf).
- My God, What Have I Done?: Grey is distraught when she accidentally kills a rabbit, being an ethical vegan. She's devastated to learn she killed her girlfriend Charlie in wolf shape later as well.
- Never Suicide: Greta, Vaughn's wife, shot herself according to him. He later admits he'd killed her, but claims it was self-defense. Given just how murderous he gets revealed as however, this is dubious.
- One-Word Title: Bloodthirsty.
- Only Sane Man: Charlie repeatedly urges Grey to leave Vaughn's house, not only before they go but after things start to go wrong after they arrived. Grey ignores this.
- Our Werewolves Are Different: They can change at will after coming to grips with their nature it seems, and there's no sign they're affected by the moon's phases. It's a hereditary condition, passed by parent to child. They can also be killed with ordinary weapons, rather than things such as silver being required.
- Parental Abandonment: Grey was given up for adoption early on. It turns out that her birth mother is dead, and she later kills her birth father.
- Patricide: Grey kills Vaughn, her birth father, to stop him murdering ever again near the end.
- The Social Darwinist: Vaughn tells Grey that only the strong survive in the world, urging her to prove her strength through crushing a mouse in her hand (she does after initial hesitation). Later he justifies killing humans by saying it was really "culling", as they're overpopulated.
- Title Drop: At the end, Grey sings a song about how she's bloodthirsty.
- The Tooth Hurts: One of Grey's teeth comes loose, which she pulls out, as a result of the changes she's now experiencing.
- Trailers Always Spoil: The trailer outright states that it's a werewolf movie, explicitly shows Grey's transformation, and even has a howl heard at the end. This is in spite of Grey's lycanthropy meaning to be a big reveal on why she has her visions and cravings in the first place.
- Transformation Sequence: Grey turns into a wolf finally near the end in an extended sequence that shows her body warping painfully. Vaughn later partially changes too before Grey shoots him.
- Twofer Token Minority: Grey's girlfriend Charlie (who's a lesbian like her), is of East Asian descent. She's the only person of color in the film.
